cmov: fix provided `Cmov::cmovz` impl (#1351) #2084

Job	Run time
build (stable, wasm32-unknown-unknown)	16s
test (1.85.0)	21s
build (1.85.0, thumbv7em-none-eabi)	18s
test (stable)	28s
build (1.85.0, wasm32-unknown-unknown)	19s
minimal-versions / minimal-versions	21s
build (stable, thumbv7em-none-eabi)	21s
	2m 24s

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