Bump proptest from 1.3.1 to 1.4.0 #3983

Job	Run time
Check	26s
Check if cbindgen runs cleanly for generating the C headers	1m 16s
coverage	2m 40s
Lints (beta)	28s
minimum_rust_version	3m 51s
Lints (stable)	29s
Publish (dry-run)	29s
test (beta)	1m 23s
test_all_features	9m 45s
test (stable)	1m 27s
Check if wasm-pack builds a valid package for the sourmash crate	1m 27s
Run tests under wasm32-wasi	1m 15s
test (windows)	2m 48s
test (macos)	4m 8s
	31m 52s

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