base32ct+base64ct: unpin `proptest`; MSRV 1.65 #2926

Job	Run time
build (1.72.0, thumbv7em-none-eabi)	38s
build (1.72.0, wasm32-unknown-unknown)	45s
build (stable, thumbv7em-none-eabi)	1m 13s
minimal-versions	0s
build (stable, wasm32-unknown-unknown)	33s
test (1.72.0)	1m 30s
test (stable)	1m 40s
	6m 19s

Provide feedback