Bump bytecount from 0.6.3 to 0.6.4 #3858

Job	Run time
Check	28s
Check if cbindgen runs cleanly for generating the C headers	2m 10s
coverage	4m 0s
Lints (beta)	54s
minimum_rust_version	5m 2s
Publish (dry-run)	46s
Lints (stable)	31s
test (beta)	2m 25s
test (stable)	2m 45s
Run tests under wasm32-wasi	2m 41s
test (windows)	6m 19s
test_all_features	15m 51s
Check if wasm-pack builds a valid package for the sourmash crate	1m 39s
test (macos)	3m 40s
	49m 11s

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