Bump actions/checkout from 3 to 4 #21

Job	Run time
test (ubuntu-latest, 27.2, false)	2m 21s
test (ubuntu-latest, 28.2, false)	6m 27s
test (ubuntu-latest, 29.1, false)	7m 9s
test (macos-latest, 27.2, false)	18m 23s
test (macos-latest, 28.2, false)	6m 41s
test (macos-latest, 29.1, false)	6m 40s
test (windows-latest, 27.2, false)	1m 37s
test (windows-latest, 28.2, false)	1m 17s
test (windows-latest, 29.1, false)	1m 12s
test (ubuntu-latest, snapshot, true)	1m 54s
test (macos-latest, snapshot, true)	6m 39s
test (windows-latest, snapshot, true)	59s
	1h 1m 19s

Provide feedback