base32ct+base64ct: unpin `proptest`; MSRV 1.65 #1417

Job	Run time
build (1.70.0, thumbv7em-none-eabi)	33s
build (1.70.0, wasm32-unknown-unknown)	40s
test (1.70.0)	1m 33s
build (stable, thumbv7em-none-eabi)	28s
test (stable)	1m 36s
build (stable, wasm32-unknown-unknown)	32s
minimal-versions / minimal-versions	1m 5s
	6m 27s

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