MRG: fix `multigather` output by adding md5sum along with `-U/--output-add-query-md5sum` #4683

Job	Run time
Check	28s
coverage	9m 52s
test (beta)	1m 33s
test_all_features	11m 14s
test (stable)	1m 33s
test (windows)	3m 16s
test (macos)	2m 22s
Check if cbindgen runs cleanly for generating the C headers	49s
Lints (beta)	36s
minimum_rust_version	9m 42s
Lints (stable)	29s
Publish (dry-run)	5m 59s
Run tests under wasm32-wasi	1m 34s
Check if wasm-pack builds a valid package for the sourmash crate	1m 24s
	50m 51s

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