sha3: bump `keccak` dependency to v0.2.0-pre.0 #171

Job	Run time
set-msrv / set-msrv	3s
minimal-versions / minimal-versions	25s
build (1.71.0, thumbv7em-none-eabi)	20s
test (1.71.0)	32s
build (1.71.0, wasm32-unknown-unknown)	20s
test (stable)	24s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	25s
	2m 48s

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