Bump `cipher` to v0.5.0-pre.6 #212

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	1m 55s
build (1.65.0, wasm32-unknown-unknown)	2m 1s
build (stable, thumbv7em-none-eabi)	15s
test (1.65.0)	2m 5s
test (stable)	21s
build (stable, wasm32-unknown-unknown)	14s
minimal-versions / minimal-versions	27s
	7m 18s

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