Bump serde from 1.0.204 to 1.0.208 #164

Job	Run time
set-image	1s
clippy	1m 37s
fmt	1m 5s
checks	1m 25s
bench-rust-nightly (bit-vec)	17m 50s
bench-rust-nightly (bytes)	16m 49s
miri (bit-vec)	5h 30m 10s
tests	2m 51s
miri (bytes)	3m 7s
bench-rust-nightly (generic-array)	17m 1s
bench-rust-nightly (derive)	16m 54s
miri (generic-array)	3m 5s
bench-rust-nightly (max-encoded-len)	16m 55s
miri (arbitrary)	3m 9s
build-linux-ubuntu-amd64	1m 21s
publish-dry-run	1m 10s
	7h 14m 30s

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