diff --git a/moto/secretsmanager/utils.py b/moto/secretsmanager/utils.py
--- a/moto/secretsmanager/utils.py
+++ b/moto/secretsmanager/utils.py
@@ -64,7 +64,7 @@ def random_password(
 
 
 def secret_arn(region, secret_id):
-    id_string = "".join(random.choice(string.ascii_letters) for _ in range(5))
+    id_string = "".join(random.choice(string.ascii_letters) for _ in range(6))
     return "arn:aws:secretsmanager:{0}:{1}:secret:{2}-{3}".format(
         region, get_account_id(), secret_id, id_string
     )

diff --git a/tests/test_secretsmanager/test_secretsmanager.py b/tests/test_secretsmanager/test_secretsmanager.py
--- a/tests/test_secretsmanager/test_secretsmanager.py
+++ b/tests/test_secretsmanager/test_secretsmanager.py
@@ -2,6 +2,7 @@
 
 import boto3
 from dateutil.tz import tzlocal
+import re
 
 from moto import mock_secretsmanager, mock_lambda, settings
 from moto.core import ACCOUNT_ID
@@ -26,6 +27,22 @@ def test_get_secret_value():
     assert result["SecretString"] == "foosecret"
 
 
+@mock_secretsmanager
+def test_secret_arn():
+    region = "us-west-2"
+    conn = boto3.client("secretsmanager", region_name=region)
+
+    create_dict = conn.create_secret(
+        Name=DEFAULT_SECRET_NAME,
+        SecretString="secret_string",
+    )
+    assert re.match(
+        f"arn:aws:secretsmanager:{region}:{ACCOUNT_ID}:secret:{DEFAULT_SECRET_NAME}-"
+        + r"\w{6}",
+        create_dict["ARN"],
+    )
+
+
 @mock_secretsmanager
 def test_create_secret_with_client_request_token():
     conn = boto3.client("secretsmanager", region_name="us-west-2")

Secret ARNs should have 6 random characters at end, not 5
When you create a secret in AWS secrets manager, the ARN is what you'd expect, plus `-xxxxxx`, where `x` is random characters.

Moto already adds random characters, but 5 instead of 6 (excluding the hyphen).

For context, I'm testing code which is asserting that the ARN of a secret matches an expected secret name. So I'm checking these characters with regex.

Run this code with and without the `.start()` line commented out.

```
import boto3
from moto import mock_secretsmanager

#mock_secretsmanager().start()

secret_name = 'test/moto/secret'

client = boto3.client('secretsmanager')

response = client.create_secret(
    Name=secret_name,
    SecretString='abc',
)
arn = response['ARN']

client.delete_secret(
    SecretId=arn,
    RecoveryWindowInDays=7,
)


print(f"arn: {arn}")
```

Expected result (i.e. result with `.start()` commented out)

```
arn: arn:aws:secretsmanager:ap-southeast-2:1234:secret:test/moto/secret-1yUghW
```

note that `1yUghW` is 6 characters.

Actual result (using moto):

```
arn: arn:aws:secretsmanager:ap-southeast-2:123456789012:secret:test/moto/secret-MoSlv
```
Note that `MoSlv` is 5 characters.

I think the problem is this line:

https://github.com/spulec/moto/blob/c82b437195a455b735be261eaa9740c4117ffa14/moto/secretsmanager/utils.py#L67

Can someone confirm that, so I can submit a PR?

tests/test_secretsmanager/test_secretsmanager.py::test_secret_arn
tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_that_has_no_value tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_value_by_arn tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_with_KmsKeyId tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_updates_last_changed_dates[True] tests/test_secretsmanager/test_secretsmanager.py::test_get_random_exclude_lowercase tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_puts_new_secret tests/test_secretsmanager/test_secretsmanager.py::test_tag_resource[False] tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_with_client_request_token tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_value_that_is_marked_deleted tests/test_secretsmanager/test_secretsmanager.py::test_untag_resource[False] tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_client_request_token_too_short tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_value tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_which_does_not_exit tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_force tests/test_secretsmanager/test_secretsmanager.py::test_get_random_password_default_requirements tests/test_secretsmanager/test_secretsmanager.py::test_describe_secret tests/test_secretsmanager/test_secretsmanager.py::test_after_put_secret_value_version_stages_can_get_current_with_custom_version_stage tests/test_secretsmanager/test_secretsmanager.py::test_update_secret[True] tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_force_no_such_secret_with_invalid_recovery_window tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_version_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_create_secret_with_client_request_token tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret tests/test_secretsmanager/test_secretsmanager.py::test_create_and_put_secret_binary_value_puts_new_secret tests/test_secretsmanager/test_secretsmanager.py::test_create_secret_with_tags_and_description tests/test_secretsmanager/test_secretsmanager.py::test_get_random_exclude_punctuation tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_updates_last_changed_dates[False] tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_enable_rotation tests/test_secretsmanager/test_secretsmanager.py::test_get_random_require_each_included_type tests/test_secretsmanager/test_secretsmanager.py::test_update_secret[False] tests/test_secretsmanager/test_secretsmanager.py::test_can_list_secret_version_ids tests/test_secretsmanager/test_secretsmanager.py::test_restore_secret tests/test_secretsmanager/test_secretsmanager.py::test_get_random_exclude_numbers tests/test_secretsmanager/test_secretsmanager.py::test_create_secret_with_description tests/test_secretsmanager/test_secretsmanager.py::test_get_random_too_short_password tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_fails_with_both_force_delete_flag_and_recovery_window_flag tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_that_does_not_match tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_force_no_such_secret tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_version_stages_response tests/test_secretsmanager/test_secretsmanager.py::test_get_random_exclude_characters_and_symbols tests/test_secretsmanager/test_secretsmanager.py::test_secret_versions_to_stages_attribute_discrepancy tests/test_secretsmanager/test_secretsmanager.py::test_get_random_include_space_true tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_describe_secret_with_arn tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_create_secret_with_tags tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_marked_as_deleted_after_restoring tests/test_secretsmanager/test_secretsmanager.py::test_untag_resource[True] tests/test_secretsmanager/test_secretsmanager.py::test_restore_secret_that_is_not_deleted tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_can_get_first_version_if_put_twice tests/test_secretsmanager/test_secretsmanager.py::test_after_put_secret_value_version_stages_pending_can_get_current tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_with_tags_and_description tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_client_request_token_too_long tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_rotation_period_zero tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_value_binary tests/test_secretsmanager/test_secretsmanager.py::test_tag_resource[True] tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_force_with_arn tests/test_secretsmanager/test_secretsmanager.py::test_describe_secret_that_does_not_match tests/test_secretsmanager/test_secretsmanager.py::test_create_secret tests/test_secretsmanager/test_secretsmanager.py::test_get_secret_that_does_not_match tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_recovery_window_too_short tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_binary_requires_either_string_or_binary tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_version_stages_pending_response tests/test_secretsmanager/test_secretsmanager.py::test_update_secret_marked_as_deleted tests/test_secretsmanager/test_secretsmanager.py::test_describe_secret_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_get_random_password_default_length tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_that_is_marked_deleted tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_binary_value_puts_new_secret tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_by_arn tests/test_secretsmanager/test_secretsmanager.py::test_get_random_exclude_uppercase tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_that_is_marked_deleted tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_rotation_lambda_arn_too_long tests/test_secretsmanager/test_secretsmanager.py::test_get_random_include_space_false tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_on_non_existing_secret tests/test_secretsmanager/test_secretsmanager.py::test_describe_secret_with_KmsKeyId tests/test_secretsmanager/test_secretsmanager.py::test_rotate_secret_rotation_period_too_long tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_versions_differ_if_same_secret_put_twice tests/test_secretsmanager/test_secretsmanager.py::test_after_put_secret_value_version_stages_can_get_current tests/test_secretsmanager/test_secretsmanager.py::test_get_random_password_custom_length tests/test_secretsmanager/test_secretsmanager.py::test_restore_secret_that_does_not_exist tests/test_secretsmanager/test_secretsmanager.py::test_put_secret_value_maintains_description_and_tags tests/test_secretsmanager/test_secretsmanager.py::test_delete_secret_recovery_window_too_long tests/test_secretsmanager/test_secretsmanager.py::test_get_random_too_long_password