chore: Removes dependencies on React <19 in tests

[pan-kot]

Updates:

• Removed the use of Simulate util from a fixture;
• Replaced ReactDOM.render() with testing-library render().

Rel: AWSUI-60345

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.92%. Comparing base (bcb5c78) to head (bdc2f36).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #80   +/-   ##
=======================================
  Coverage   95.92%   95.92%           
=======================================
  Files           9        9           
  Lines         319      319           
  Branches       68       68           
=======================================
  Hits          306      306           
  Misses         13       13           

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