rc5

Bump `cipher` to v0.5.0-pre.6 #172

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 3s
test (1.65.0)	2m 3s
build (1.65.0, wasm32-unknown-unknown)	2m 1s
test (stable)	23s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	14s
minimal-versions / minimal-versions	24s
	7m 23s

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