Bump actions/checkout from 5 to 6 #544

Job	Run time
test (ubuntu-latest, 30.2, false)	8m 2s
test (ubuntu-latest, 28.2, false)	7m 23s
test (windows-latest, 29.4, false)	2m 42s
test (macos-latest, 28.2, false)	7m 30s
test (macos-latest, 29.4, false)	6m 32s
test (windows-latest, 28.2, false)	2m 41s
test (windows-latest, snapshot, true)	1m 47s
test (windows-latest, 30.2, false)	3m 24s
test (macos-latest, snapshot, true)	8m 25s
test (ubuntu-latest, 29.4, false)	7m 12s
test (macos-latest, 30.2, false)	8m 13s
test (ubuntu-latest, snapshot, true)	8m 0s
	1h 11m 51s

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