Prep to release 3.7.0 #274

Job	Run time
set-image	1s
tests	1m 51s
checks	1m 13s
clippy	1m 25s
fmt	50s
bench-rust-nightly (bit-vec)	18m 8s
miri (bit-vec)	3h 50m 14s
miri (bytes)	3m 7s
miri (generic-array)	3m 6s
miri (arbitrary)	3m 14s
bench-rust-nightly (bytes)	17m 11s
bench-rust-nightly (generic-array)	17m 11s
bench-rust-nightly (derive)	17m 32s
bench-rust-nightly (max-encoded-len)	17m 9s
build-linux-ubuntu-amd64	1m 12s
publish-dry-run	1m 7s
	5h 34m 31s

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