Bump version to 21.7.0 #4220

Job	Run time
build-fuzz	2m 50s
cargo-deny (advisories)	37s
check-git-rev-deps	14s
build-and-test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	7m 24s
cargo-deny (bans licenses sources)	38s
docs	4m 18s
build-and-test (msrv, ubuntu-latest, aarch64-unknown-linux-gnu, true)	4m 44s
build-and-test (msrv, windows-latest, x86_64-pc-windows-msvc)	15m 58s
fmt	13s
build-and-test (latest, ubuntu-latest, x86_64-unknown-linux-gnu)	7m 6s
readme	4m 49s
build-and-test (latest, ubuntu-latest, aarch64-unknown-linux-gnu, true)	4m 26s
semver-checks	5m 22s
build-and-test (latest, windows-latest, x86_64-pc-windows-msvc)	16m 53s
publish-dry-run (ubuntu-latest, x86_64-unknown-linux-gnu, --feature-powerset --exclude-features d... / publish-dry-run / publish-dry-run	5m 48s
publish-dry-run (ubuntu-latest, wasm32-unknown-unknown) / publish-dry-run / publish-dry-run	4m 36s
complete	1s
	1h 25m 57s

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