Test Gradle on Windows

[blasten]

Enable Gradle tests on Windows.
I chatted with @dnfield about this a while back.

Fixes #36311

[fluttergithubbot]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[codecov]

Codecov Report

Merging #42709 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #42709      +/-   ##
==========================================
- Coverage   61.23%   61.22%   -0.02%     
==========================================
  Files         195      195              
  Lines       18954    18954              
==========================================
- Hits        11606    11604       -2     
- Misses       7348     7350       +2

Flag	Coverage Δ
#flutter_tool	61.22% <ø> (-0.02%)	⬇️

Impacted Files	Coverage Δ
...kages/flutter_tools/lib/src/commands/generate.dart	11.11% <0%> (-74.08%)	⬇️
...ckages/flutter_tools/lib/src/commands/channel.dart	43.07% <0%> (-29.24%)	⬇️
packages/flutter_tools/lib/src/base/build.dart	60.5% <0%> (-15.13%)	⬇️
...ges/flutter_tools/lib/src/build_system/source.dart	79.59% <0%> (-4.09%)	⬇️
packages/flutter_tools/lib/src/base/terminal.dart	77.92% <0%> (-3.9%)	⬇️
packages/flutter_tools/lib/src/codegen.dart	5.63% <0%> (-1.41%)	⬇️
packages/flutter_tools/lib/src/compile.dart	77.89% <0%> (-0.69%)	⬇️
packages/flutter_tools/lib/src/base/logger.dart	82.75% <0%> (-0.39%)	⬇️
packages/flutter_tools/lib/src/cache.dart	48.47% <0%> (-0.24%)	⬇️
packages/flutter_tools/lib/src/vmservice.dart	41.5% <0%> (+0.33%)	⬆️
... and 4 more

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[mklim]

Code itself LGTM, RSLGTM for Windows no longer crashing. :)