chore(deps): update proptest requirement from =1.5 to =1.6 #937

Job	Run time
Cargo deny check	18s
Clippy	50s
Feature checks	32s
Docs	52s
Fmt	12s
test (stable, --no-default-features)	1m 11s
test (stable)	1m 7s
test (stable, --all-features)	2m 15s
test (beta, --no-default-features)	1m 19s
test (beta)	1m 26s
test (beta, --all-features)	2m 25s
test (nightly, --no-default-features)	1m 11s
test (nightly)	1m 17s
test (nightly, --all-features)	2m 4s
test (1.65, --no-default-features)	22s
test (1.65)	28s
Accept	0s
	17m 49s

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