GitHub Actions: Add testing on Windows

[cclauss]

Currently testing on Windows is commented out in our GitHub Actions.

python-magic/.github/workflows/ci.yml

Lines 13 to 14 in aa49677

	# - os: windows-latest # TODO: Fix the Windows test that runs in an infinite loop
	# python-version: '3.13'

Linux and macOS work just fine but on Windows the tests never complete.

[ddelange]

here are the pytest failues on windows: #294 (comment)

when they're fixed (or skipped), we could re-introduce pytest in wheels.yml (84667ee) to get proper platform tests:

• ci.yml would run pytest for different python versions (linux only)
• wheels.yml would run pytest for different (emulated) cpu architectures and operating systems (including the different mac and windows flavours)

[cclauss]

I prefer a test job that runs the tests.
And a separate wheels / deployment job that is focused on moving to production. However I don’t want to do anything that slows down this PR.