cmov: docs fix: array => slice #209

Job	Run time
test-careful	1m 22s
test (1.85.0)	1m 9s
test-miri (s390x-unknown-linux-gnu)	1m 4s
test (stable)	1m 6s
build (1.85.0, thumbv7em-none-eabi)	17s
build (1.85.0, wasm32-unknown-unknown)	18s
build (stable, wasm32-unknown-unknown)	15s
test-miri (x86_64-unknown-linux-gnu)	48s
build (stable, thumbv7em-none-eabi)	14s
	6m 33s

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