Add coe coverage for RadioButtonFlatAdapter

[Zheng-Li01]

Related #13442

Proposed changes

Add unit test file:RadioButtonFlatAdapterTests.cs for public/protected methods/properties of the RadioButtonFlatAdapter.cs

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 93.05556% with 15 lines in your changes missing coverage. Please review.

Project coverage is 76.93672%. Comparing base (7c04597) to head (7bd412b).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13727         +/-   ##
===================================================
+ Coverage   76.90689%   76.93672%   +0.02982%     
===================================================
  Files           3260        3261          +1     
  Lines         643088      643304        +216     
  Branches       47601       47628         +27     
===================================================
+ Hits          494579      494937        +358     
+ Misses        144845      144691        -154     
- Partials        3664        3676         +12     

Flag	Coverage Δ
Debug	76.93672% <93.05556%> (+0.02982%)	⬆️
integration	18.99173% <ø> (+0.00383%)	⬆️
production	51.63017% <ø> (+0.05456%)	⬆️
test	97.41887% <93.05556%> (-0.00266%)	⬇️
unit	49.01168% <ø> (+0.05211%)	⬆️

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[Zheng-Li01]

Closed this PR due to the #13456 have been created.