Rust

ci: Update to `actions/checkout@v4`. #299

Job	Run time
Benchmarks (criterion)	10m 28s
Lints, pinned toolchain	4m 10s
Build, minimum toolchain	5m 12s
Tests, unstable toolchain (beta)	1m 18s
Tests, unstable toolchain (nightly)	1m 18s
Tests, stable toolchain	1m 52s
	24m 18s

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