Fix parameterized UI tests for WinUI

[Youssef1313]

We should pass null so that we fallback to Arguments which has the right thing for parameterized tests:

testfx/src/Adapter/MSTest.TestAdapter/Execution/TestMethodInfo.cs

Line 149 in d991da7

arguments ??= Arguments;

Fixes #740

It looks like we don't have the test infra that allows to test this, as we need vstest.console.exe that comes with VS. It should be possible to test it, but requires a bit of test infra work.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.91%. Comparing base (d991da7) to head (a6c5074).

Files with missing lines	Patch %	Lines
...tensions/Attributes/WinUI_UITestMethodAttribute.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5305      +/-   ##
==========================================
- Coverage   75.28%   72.91%   -2.38%     
==========================================
  Files         601      601              
  Lines       37673    37672       -1     
==========================================
- Hits        28363    27469     -894     
- Misses       9310    10203     +893     

Flag	Coverage Δ
Debug	72.91% <0.00%> (-2.38%)	⬇️
integration	72.91% <0.00%> (-2.38%)	⬇️
production	72.91% <0.00%> (-2.38%)	⬇️
unit	72.91% <0.00%> (-2.38%)	⬇️

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Files with missing lines	Coverage Δ
...tensions/Attributes/WinUI_UITestMethodAttribute.cs	0.00% <0.00%> (ø)

... and 62 files with indirect coverage changes

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