sha3: bump `keccak` dependency to v0.2.0-pre.0 #572

Job	Run time
minimal-versions / minimal-versions	57s
set-msrv / set-msrv	3s
build (1.71.0, thumbv7em-none-eabi)	20s
test (1.71.0)	55s
build (1.71.0, wasm32-unknown-unknown)	19s
build (stable, thumbv7em-none-eabi)	14s
test (stable)	41s
build (stable, wasm32-unknown-unknown)	13s
	3m 42s

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