base32ct+base64ct: unpin `proptest`; MSRV 1.65 #2998

Job	Run time
minimal-versions	0s
build (1.72.0, thumbv7em-none-eabi)	28s
build (1.72.0, wasm32-unknown-unknown)	27s
build (stable, thumbv7em-none-eabi)	25s
test (1.72.0)	1m 22s
build (stable, wasm32-unknown-unknown)	30s
test (stable)	1m 7s
	4m 19s

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