Bump `cipher` to v0.5.0-pre.6 (#430) #213

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 5s
build (1.65.0, wasm32-unknown-unknown)	1m 59s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	13s
test (1.65.0)	2m 4s
test (stable)	23s
minimal-versions / minimal-versions	28s
	7m 27s

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