Do not run CI on beta or nightly #13

Job	Run time
windows-build-and-test-msrv / build-and-test	3m 41s
windows-build-and-test-stable / build-and-test	3m 49s
windows-lint-stable / lint	3m 3s
windows-coverage-stable / coverage	1m 56s
	12m 29s

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