Bump serde from 1.0.215 to 1.0.216 #6118

Job	Run time
Check	23s
coverage	10m 41s
Lints (beta)	34s
Lints (stable)	42s
test_all_features	14m 0s
test (beta)	1m 33s
test (stable)	1m 26s
Check if wasm-pack builds a valid package for the sourmash crate	1m 24s
Check if cbindgen runs cleanly for generating the C headers	8m 54s
minimum_rust_version	7m 24s
test (windows)	4m 15s
test (macos)	1m 24s
Publish (on tags, dry-run otherwise)	5m 45s
Run tests under wasm32-wasi	1m 22s
	59m 47s

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