Bump actions/checkout from 3 to 4 #65

Job	Run time
test (ubuntu-latest, 27.2, false)	47s
test (ubuntu-latest, 28.2, false)	56s
test (ubuntu-latest, 29.1, false)	53s
test (macos-latest, 27.2, false)	4m 12s
test (macos-latest, 28.2, false)	3m 31s
test (macos-latest, 29.1, false)	3m 0s
test (windows-latest, 27.2, false)	1m 27s
test (windows-latest, 28.2, false)	1m 27s
test (windows-latest, 29.1, false)	1m 25s
test (ubuntu-latest, snapshot, true)	42s
test (macos-latest, snapshot, true)	13m 21s
test (windows-latest, snapshot, true)	1m 22s
	33m 3s

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