[NO MERGE] use a hacky way to run all the tests using new FileStream implementation

[adamsitnik]

Please ignore this PR, I just want to check if the most recent changes have not broken anything in WinForms before we enable them by default.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Merging #4756 (aae8fef) into main (3b50903) will decrease coverage by 0.00752%.
The diff coverage is n/a.

❗ Current head aae8fef differs from pull request most recent head 859447b. Consider uploading reports for the commit 859447b to get more accurate results

@@                 Coverage Diff                 @@
##                main       #4756         +/-   ##
===================================================
- Coverage   97.96231%   97.95479%   -0.00752%     
===================================================
  Files            547         547                 
  Lines         266036      266036                 
  Branches        5109        5109                 
===================================================
- Hits          260615      260595         -20     
- Misses          4531        4547         +16     
- Partials         890         894          +4     

Flag	Coverage Δ
Debug	97.95479% <ø> (-0.00752%)	⬇️
test	97.95479% <ø> (-0.00752%)	⬇️

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[adamsitnik]

The change in runtime repo (dotnet/runtime#50166) has been merged, I am closing the PR.