chore: Format files for the Dart 3.13 formatter

[VarshithaPamisetty]

Description:

The stable Dart formatter (3.13) reformats amplify_auth_cognito/example/integration_test/sign_in_test.dart (plus the amplify_analytics_pinpoint example, and aft / amplify_test source).

Tests

• dart format clean on the packages with Flutter 3.47.0 / Dart 3.13 (format_check exits 0).
• Diff is formatting-only (reproducible from the formatter).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.98%. Comparing base (b0c2048) to head (411d42b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7276      +/-   ##
==========================================
+ Coverage   40.97%   40.98%   +0.01%     
==========================================
  Files         121      121              
  Lines        8273     8273              
  Branches     3598     3598              
==========================================
+ Hits         3390     3391       +1     
+ Misses       4883     4882       -1     

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