Bump version to 21.7.4 #4358

Job	Run time
cargo-deny (advisories)	38s
build-fuzz	5m 30s
cargo-deny (bans licenses sources)	38s
check-git-rev-deps	7s
build-and-test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	13m 31s
docs	5m 35s
build-and-test (msrv, ubuntu-latest, aarch64-unknown-linux-gnu, true)	8m 31s
fmt	13s
build-and-test (msrv, windows-latest, x86_64-pc-windows-msvc)	17m 56s
readme	3m 17s
semver-checks	5m 47s
build-and-test (latest, ubuntu-latest, x86_64-unknown-linux-gnu)	12m 43s
build-and-test (latest, ubuntu-latest, aarch64-unknown-linux-gnu, true)	7m 49s
build-and-test (latest, windows-latest, x86_64-pc-windows-msvc)	16m 0s
publish-dry-run (ubuntu-latest, wasm32-unknown-unknown) / publish-dry-run / publish-dry-run	5m 39s
publish-dry-run (ubuntu-latest, x86_64-unknown-linux-gnu, --feature-powerset --exclude-features d... / publish-dry-run / publish-dry-run	6m 0s
complete	1s
	1h 49m 55s

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