ci: Update to `actions/checkout@v4` #109

Job	Run time
Check code formatting	6s
Linux (1.56.0)	2m 47s
Linux (stable)	21s
Linux (beta)	21s
Linux (nightly)	17s
Linux (--features serde, 1.56.0)	2m 52s
Linux (--features serde, stable)	17s
Linux (--features serde, beta)	24s
Linux (--features serde, nightly)	21s
Linux (--no-default-features --features libm, 1.56.0)	2m 54s
Linux (--no-default-features --features libm, stable)	12s
Linux (--no-default-features --features libm, beta)	21s
Linux (--no-default-features --features libm, nightly)	19s
Linux (stable, --features mint)	11s
Linux (stable, --features bytemuck)	23s
Linux (stable, --features arbitrary)	19s
Linux (nightly, --features unstable)	17s
Linux (nightly, --features unstable,serde)	22s
Result	1s
	13m 5s

Provide feedback