Update actions/checkout action to v4 #243

Job	Run time
mock-plan (examples/complete)	1m 57s
mock-plan (examples/no-cert)	1m 45s
mock-plan (examples/no-cert-no-hosted-zone)	1m 31s
mock-plan (examples/no-hosted-zone)	1m 52s
mock-plan (examples/ordered-cache-behavior)	1m 31s
validate (examples/complete)	32s
validate (examples/no-cert)	34s
validate (examples/no-cert-no-hosted-zone)	39s
validate (examples/no-hosted-zone)	29s
validate (examples/ordered-cache-behavior)	40s
check-format	12s
Show infracost diff (examples/complete)	29s
Show infracost diff (examples/no-cert)	25s
Show infracost diff (examples/no-cert-no-hosted-zone)	27s
Show infracost diff (examples/no-hosted-zone)	27s
Show infracost diff (examples/ordered-cache-behavior)	32s
	14m 2s

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