Run tests in Windows

[busunkim96]

CI currently only runs in a linux environment in the python repositories.

Resources:

• NodeJS has some Windows tests:
  • https://github.com/googleapis/nodejs-storage/pull/1321/checks?check_run_id=1349742576
• gRPC has Windows tests.

Issues:

• Appropriate docker images.
• Build scripts (maybe not if we just run nox)

A good first step might be to get tests running on the gapic-generator-python repo to catch common issues in the generated surface. https://github.com/googleapis/gapic-generator-python

[tswast]

Once every couple of years I see a bug that is Windows-only. e.g. https://github.com/googleapis/python-bigquery-pandas/issues/119 and https://github.com/googleapis/python-bigquery-storage/issues/4, so I think this would have some value to our customers. Especially since few of us develop on Windows.