ci: update `actions/checkout` to `v4` #225

Job	Run time
audit	11s
formatting	8s
build-and-test (ubuntu-latest, stable)	1m 23s
linting	31s
build-and-test (ubuntu-latest, beta)	1m 14s
build-and-test (macos-latest, stable)	1m 5s
build-and-test (macos-latest, beta)	1m 9s
build-and-test (windows-latest, stable)	3m 47s
build-and-test (windows-latest, beta)	3m 2s
build-and-test (ubuntu-latest, nightly)	1m 1s
build-and-test (ubuntu-latest, 1.77.0)	1m 14s
	14m 45s

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