sha3: bump `keccak` dependency to v0.2.0-pre.0 #620

Job	Run time
minimal-versions / minimal-versions	29s
set-msrv / set-msrv	3s
build (1.74.0, thumbv7em-none-eabi)	19s
test (1.74.0)	29s
build (1.74.0, wasm32-unknown-unknown)	19s
build (stable, thumbv7em-none-eabi)	14s
build (stable, wasm32-unknown-unknown)	14s
test (stable)	17s
	2m 24s

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