Update cache action to v4 #273

Job	Run time
cargo clippy	1m 34s
test-executors-no-ws-timed-fairness (stable)	1m 43s
cargo fmt	1m 30s
test-executors-no-ws-timed-fairness (nightly)	1m 35s
test-executors-misc-features (stable, ws-no-park)	1m 41s
tests (stable)	1m 39s
test-executors-misc-features (stable, thread-pinning)	1m 40s
tests (nightly)	1m 31s
test-executors-misc-features (stable, numa-aware)	1m 41s
test-executors-misc-features (stable, produce-metrics)	1m 47s
test-executors-misc-features (nightly, ws-no-park)	1m 36s
test-executors-misc-features (nightly, thread-pinning)	1m 35s
test-executors-misc-features (nightly, numa-aware)	1m 35s
test-executors-misc-features (nightly, produce-metrics)	1m 31s
	22m 38s

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