Update actions/checkout action to v4 (#2495) #4292

Job	Run time
cargo-hack	4m 52s
check	1m 23s
check-docs	38s
cargo-public-api-crates (axum)	1m 0s
cargo-public-api-crates (axum-core)	46s
cargo-deny check (advisories)	23s
dependencies-are-sorted	13s
cargo-public-api-crates (axum-extra)	54s
Spell Check with Typos	8s
cargo-deny check (bans licenses sources)	23s
cargo-public-api-crates (axum-macros)	50s
test-nightly	2m 15s
test-docs	1m 58s
armv5te-unknown-linux-musleabi	47s
test-versions (stable)	2m 57s
test-msrv	4m 56s
test-versions (beta)	3m 25s
wasm32-unknown-unknown	24s
	28m 12s

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