Update actions/checkout action to v6 #2205

Job	Run time
check	4m 9s
bazel	1m 25s
Docker CLI tests (ubuntu-latest)	6m 31s
Maven tests (21)	2m 27s
bazel_aspect	3m 3s
Tests (ubuntu-latest, 11)	13m 34s
Tests (ubuntu-latest, 8)	6h 5m 0s
Maven tests (8)	2m 25s
Maven tests (11)	2m 30s
Maven tests (17)	2m 31s
Tests (ubuntu-latest, 17)	11m 16s
Tests (ubuntu-latest, 21)	7m 4s
	7h 1m 55s

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