base32ct+base64ct: unpin `proptest`; MSRV 1.65 #1185

Job	Run time
minimal-versions	0s
build (1.75.0, thumbv7em-none-eabi)	36s
build (1.75.0, wasm32-unknown-unknown)	34s
test (1.75.0)	7m 35s
test (stable)	6m 44s
build (stable, thumbv7em-none-eabi)	32s
build (stable, wasm32-unknown-unknown)	24s
	16m 25s

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