Update actions/checkout action to v4 #2262

Job	Run time
cargo bench	1m 15s
cargo clippy	40s
cargo +stable build	1m 13s
cargo +beta build	1m 6s
cargo +nightly build	1m 1s
codegen	31s
cargo +1.36 build (futures-{core, io, sink})	2m 32s
cargo doc	32s
cargo hack check --feature-powerset	5m 14s
cargo fmt	16s
cargo minimal-versions build	38s
cargo miri test	9m 18s
cargo build --target thumbv7m-none-eabi	39s
cargo build --target thumbv6m-none-eabi	52s
cargo test -Z sanitizer=address	4m 26s
cargo test -Z sanitizer=memory	3m 47s
cargo test -Z sanitizer=thread	3m 1s
cargo test (ubuntu-latest)	4m 27s
cargo test (macos-latest)	6m 52s
cargo test (windows-latest)	6m 49s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	4m 42s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	9m 37s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	9m 14s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	4m 47s
cargo +1.56 build	2m 15s
	1h 25m 44s

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