Bump serde from 1.0.214 to 1.0.215 #266

Job	Run time
set-image	1s
checks	1m 27s
fmt	1m 11s
clippy	1m 42s
bench-rust-nightly (bit-vec)	18m 28s
bench-rust-nightly (bytes)	17m 21s
miri (bit-vec)	3h 46m 43s
tests	3m 59s
bench-rust-nightly (generic-array)	17m 49s
bench-rust-nightly (derive)	17m 29s
bench-rust-nightly (max-encoded-len)	17m 46s
miri (bytes)	3m 30s
miri (generic-array)	3m 29s
miri (arbitrary)	3m 33s
build-linux-ubuntu-amd64	1m 18s
publish-dry-run	1m 25s
	5h 37m 11s

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