Bump actions/checkout from 3 to 4 #494

Job	Run time
test (ubuntu-latest, 27.2, false)	55s
test (ubuntu-latest, 28.2, false)	48s
test (ubuntu-latest, 29.3, false)	1m 6s
test (macos-latest, 27.2, false)	2m 59s
test (macos-latest, 28.2, false)	2m 22s
test (macos-latest, 29.3, false)	3m 9s
test (windows-latest, 27.2, false)	1m 54s
test (windows-latest, 28.2, false)	1m 37s
test (windows-latest, 29.3, false)	1m 33s
test (ubuntu-latest, snapshot, true)	43s
test (macos-latest, snapshot, true)	2m 38s
test (windows-latest, snapshot, true)	2m 2s
	21m 46s

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