Bump twox-hash from 1.6.3 to 2.1.0 #6074

Job	Run time
Check	27s
test_all_features	4m 4s
coverage	8m 18s
Lints (beta)	43s
minimum_rust_version	51s
Lints (stable)	30s
Publish (on tags, dry-run otherwise)	8m 47s
test (beta)	1m 9s
Run tests under wasm32-wasi	1m 12s
test (stable)	1m 11s
Check if wasm-pack builds a valid package for the sourmash crate	1m 17s
test (windows)	3m 36s
test (macos)	1m 23s
Check if cbindgen runs cleanly for generating the C headers	9m 4s
	42m 32s

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