matrix: Fix test failure brought by the hint for usernames change.
Fixes
MODIFY
zulip/integrations/bridge_with_matrix/test_matrix.py
zulip/integrations/bridge_with_matrix/test_matrix.py
@@ -17,7 +17,7 @@ sample_config_path = "matrix_test.conf"
sample_config_text = """[matrix]
host = https://matrix.org
-username = username
+username = @username@matrix.org
password = password
room_id = #zulip:matrix.org

matrix: Fix test failure brought by the hint for usernames change.

Fixes a188a4e72a525847ded80eee6e864e43715e3bd7.