Main workflow

Builds, tests & co #54

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Run time

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Job	Run time
lint-doc	1m 54s
lint-opam	2m 11s
build (macos-latest, 4.14)	1m 58s
build (macos-latest, 5.2)	1m 55s
build (ubuntu-latest, 4.14)	1m 27s
build (ubuntu-latest, 5.2)	1m 24s
build (windows-latest, 4.14)	3m 1s
build (windows-latest, 5.2)	3m 7s
build (ubuntu-latest, 4.08)	1m 18s
	18m 15s