ci: Update to actions/checkout v6 (#3572) #5890

Job	Run time
check	44s
check-docs	38s
cargo-deny check (bans licenses sources)	23s
cargo-deny check (advisories)	30s
dependencies-are-sorted	8s
cargo-hack	2m 39s
cargo-public-api-crates (axum-extra)	53s
cargo-public-api-crates (axum-core)	45s
cargo-public-api-crates (axum-macros)	43s
Spell Check with Typos	7s
cargo-public-api-crates (axum)	58s
test-nightly	1m 4s
test-versions (beta)	1m 11s
wasm32-unknown-unknown	24s
test-docs	59s
test-versions (stable)	1m 20s
test-msrv	2m 50s
armv5te-unknown-linux-musleabi	39s
	16m 55s

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