Bump proptest from 1.5.0 to 1.6.0 #6129

Job	Run time
Check	25s
coverage	10m 55s
Check if cbindgen runs cleanly for generating the C headers	8m 51s
Lints (beta)	33s
Lints (stable)	41s
minimum_rust_version	7m 24s
Publish (on tags, dry-run otherwise)	9m 26s
test (beta)	1m 31s
test_all_features	12m 52s
test (stable)	1m 25s
Run tests under wasm32-wasi	1m 10s
test (windows)	4m 20s
Check if wasm-pack builds a valid package for the sourmash crate	1m 24s
test (macos)	1m 19s
	1h 2m 16s

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