Bump actions/checkout from 3 to 4 #1932

Job	Run time
build (2_12, mima)	1m 47s
build (2_12, e2e)	9s
build (2_12, test)	10m 35s
build (2_13, mima)	1m 25s
conformance	2m 12s
build (2_13, e2e)	14s
build (2_13, test)	15m 49s
build (3, mima)	9s
build (3, e2e)	5s
build (3, test)	14m 13s
build (2_12, examples_and_formatting)	4m 50s
build (2_13, scala3_compat_test)	12m 8s
build (3, scala3_compat_test)	15m 51s
ci-passed	1s
	1h 19m 28s

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