ci(macos): add macos-12 to cover x86_64 #186

Job	Run time
build-and-test-windows (16.x)	2m 48s
build-and-test-osx (16.x, macos-12)	2m 3s
build-and-test-windows (18.x)	2m 31s
build-and-test-ubuntu (16.x)	54s
build-and-test-windows (20.x)	3m 0s
build-and-test-ubuntu (18.x)	1m 22s
build-and-test-osx (16.x, macos-latest)	57s
build-and-test-osx (18.x, macos-12)	2m 21s
build-and-test-ubuntu (20.x)	1m 2s
build-and-test-osx (18.x, macos-latest)	1m 23s
build-and-test-osx (20.x, macos-12)	1m 50s
build-and-test-osx (20.x, macos-latest)	1m 7s
finish	2s
	21m 20s

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