ci: add windows-latest to test matrix (#65) #127

Job	Run time
pytest (ubuntu-latest)	17s
Frontend unit tests (vitest) (windows-latest)	48s
mypy	20s
API integration tests + coverage (ubuntu-latest)	13s
Verify prod requirements.txt is sufficient	9s
pytest (windows-latest)	37s
Frontend unit tests (vitest) (ubuntu-latest)	18s
API integration tests + coverage (windows-latest)	38s
	3m 20s

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