Update actions/checkout action to v4 #4291

Job	Run time
check	1m 28s
cargo-hack	5m 16s
cargo-public-api-crates (axum)	59s
check-docs	35s
cargo-public-api-crates (axum-core)	46s
cargo-deny check (advisories)	23s
cargo-public-api-crates (axum-extra)	1m 1s
dependencies-are-sorted	19s
Spell Check with Typos	5s
cargo-public-api-crates (axum-macros)	50s
cargo-deny check (bans licenses sources)	26s
test-nightly	2m 9s
test-msrv	4m 58s
armv5te-unknown-linux-musleabi	57s
test-docs	2m 1s
test-versions (stable)	3m 3s
wasm32-unknown-unknown	29s
test-versions (beta)	3m 14s
	28m 59s

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