Bump twox-hash from 1.6.3 to 2.1.0 #6070

Job	Run time
Check	25s
coverage	8m 48s
Lints (beta)	34s
Lints (stable)	30s
test (beta)	1m 16s
test (stable)	1m 4s
test (windows)	3m 31s
test_all_features	4m 3s
test (macos)	1m 13s
Check if cbindgen runs cleanly for generating the C headers	8m 55s
minimum_rust_version	50s
Publish (on tags, dry-run otherwise)	8m 56s
Run tests under wasm32-wasi	1m 23s
Check if wasm-pack builds a valid package for the sourmash crate	1m 21s
	42m 49s

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