BUG: assert_series_equal b/w datetime column  with equivalent object column  fails with `check_dtype=False` 
### 

- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [X] I have confirmed this bug exists on the master branch of pandas.


### Reproducible Example

```python
import pandas  as pd

s1 = pd.Series(['2020-01-01 00:00:00'])
s2 = pd.to_datetime(s1)
pd.testing.assert_series_equal(s1,s2,check_dtype=False)
```

```python-traceback
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/nfs/vjawa/pandas/pandas/_testing/asserters.py", line 1078, in assert_series_equal
    _testing.assert_almost_equal(
  File "pandas/_libs/testing.pyx", line 53, in pandas._libs.testing.assert_almost_equal
    cpdef assert_almost_equal(a, b,
  File "pandas/_libs/testing.pyx", line 168, in pandas._libs.testing.assert_almost_equal
    raise_assert_detail(obj, msg, lobj, robj, index_values=index_values)
  File "/home/nfs/vjawa/pandas/pandas/_testing/asserters.py", line 666, in raise_assert_detail
    raise AssertionError(msg)
AssertionError: Series are different

Series values are different (100.0 %)
[index]: [0]
[left]:  [2020-01-01 00:00:00]
[right]: <DatetimeArray>
['2020-01-01 00:00:00']
Length: 1, dtype: datetime64[ns]
```


### Issue Description

#### BUG: assert_series_equal b/w datetime column  with equivalent object column  fails with `check_dtype=False` 
When trying to compare two series where one is an object and the other is  an equivalent date-time created using   `pd.to_datetime` , we get a unexpected `AssertionError`.

### Expected Behavior

I would expect that we pass the assertion. 

### Installed Versions

<details>

INSTALLED VERSIONS
------------------
commit           : 36d5c9b8e521fea564cdc44491253f9d9c903fe9
python           : 3.9.7.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.15.0-76-generic
Version          : #86-Ubuntu SMP Fri Jan 17 17:24:28 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.4.0.dev0+745.g36d5c9b8e5
numpy            : 1.20.3
pytz             : 2021.1
dateutil         : 2.8.2
pip              : 21.2.4
setuptools       : 58.0.4
Cython           : 0.29.24
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : 1.3.2
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : 2.7.3
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
