Bump actions/checkout from 3 to 4 #538

Job	Run time
test (ubuntu-latest, 27.2, false)	1m 37s
test (ubuntu-latest, 28.2, false)	1m 10s
test (ubuntu-latest, 29.3, false)	1m 11s
test (macos-latest, 27.2, false)	2m 7s
test (macos-latest, 28.2, false)	3m 10s
test (macos-latest, 29.3, false)	2m 21s
test (windows-latest, 27.2, false)	2m 12s
test (windows-latest, 28.2, false)	1m 55s
test (windows-latest, 29.3, false)	1m 54s
test (ubuntu-latest, snapshot, true)	56s
test (macos-latest, snapshot, true)	2m 4s
test (windows-latest, snapshot, true)	32s
	21m 9s

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