fix(API): Fixing issue with CN endpoints

[ruisebas]

Issue #

• AppSync realtime endpoint URL is not correct for AWS China regions #3915

Description

This PR fixes an issue when handling CN endpoints in our AppSyncRealTimeClientFactory.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
  
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.77%. Comparing base (2a17a77) to head (001c485).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3941      +/-   ##
==========================================
- Coverage   67.77%   67.77%   -0.01%     
==========================================
  Files        1125     1125              
  Lines       52117    52117              
==========================================
- Hits        35322    35320       -2     
- Misses      16795    16797       +2     

Flag	Coverage Δ
API_plugin_unit_test	70.33% <100.00%> (ø)
AWSPluginsCore	70.36% <ø> (ø)
Amplify	47.89% <ø> (-0.07%)	⬇️
Analytics_plugin_unit_test	85.20% <ø> (ø)
Auth_plugin_unit_test	73.68% <ø> (+0.03%)	⬆️
DataStore_plugin_unit_test	83.38% <ø> (-0.03%)	⬇️
Geo_plugin_unit_test	74.86% <ø> (ø)
Logging_plugin_unit_test	63.11% <ø> (ø)
Predictions_plugin_unit_test	35.49% <ø> (ø)
PushNotifications_plugin_unit_test	88.43% <ø> (ø)
Storage_plugin_unit_test	76.88% <ø> (ø)
unit_tests	67.77% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.