Bump actions/checkout from 3 to 4 #85

Job	Run time
test (ubuntu-latest, 26.3, false)	38s
test (ubuntu-latest, 27.2, false)	35s
test (ubuntu-latest, 28.2, false)	37s
test (ubuntu-latest, 29.4, false)	1m 7s
test (ubuntu-latest, 30.1, false)	54s
test (macos-latest, 28.2, false)	1m 28s
test (macos-latest, 29.4, false)	1m 50s
test (macos-latest, 30.1, false)	2m 6s
test (windows-latest, 26.3, false)	4m 19s
test (windows-latest, 27.2, false)	2m 45s
test (windows-latest, 28.2, false)	2m 24s
test (windows-latest, 29.4, false)	3m 17s
test (windows-latest, 30.1, false)	1m 55s
test (ubuntu-latest, snapshot, true)	33s
test (macos-latest, snapshot, true)	1m 35s
test (windows-latest, snapshot, true)	4m 40s
	30m 43s

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