Fix git hooks on Windows

[loic-sharma]

Windows does not pre-install python3. Previously Windows users would just use Python from depot tools, but this was broken by #51156.

[flutter-dashboard]

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If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

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[zanderso]

Whoops. Can you verify that this still works on mac and Linux?

[loic-sharma]

@zanderso Verified.

• Linux
  • post-checkout
  • post-merge
  • pre-rebase
  • pre-push

    • ⚠️ On a clean Linux machine this throws:

      Checking Python formatting...
      To fix, run `et format` or:
      
      git apply <<DONE
        /home/loic/code/f/engine/src/flutter/tools/gn
      Traceback (most recent call last):
        File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
          return _run_code(code, main_globals, None,
        File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
          exec(code, run_globals)
        File "/home/loic/code/f/engine/src/flutter/third_party/yapf/yapf/__main__.py", line 16, in <module>
          import yapf
        File "/home/loic/code/f/engine/src/flutter/third_party/yapf/yapf/__init__.py", line 35, in <module>
          from yapf.yapflib import errors
        File "/home/loic/code/f/engine/src/flutter/third_party/yapf/yapf/yapflib/errors.py", line 16, in <module>
          from lib2to3.pgen2 import tokenize
      ModuleNotFoundError: No module named 'lib2to3'
      
      DONE
      
      Checking for trailing whitespace on 1 source file...
      
      

• macOS
  • post-checkout
  • post-merge
  • pre-rebase
  • pre-push

Sorry for the delay, I didn't have a Linux machine setup at the office.

[zanderso]

Thanks!

[Hixie]

test-exempt: we'll find out about this being broken really quickly when it matters