hkdf

Bump `digest` to v0.11.0-pre.9 (#98) #177

Job	Run time
build (1.72.0, thumbv7em-none-eabi)	21s
build (1.72.0, wasm32-unknown-unknown)	20s
build (stable, thumbv7em-none-eabi)	18s
build (stable, wasm32-unknown-unknown)	19s
minimal-versions	0s
test (1.72.0)	24s
test (stable)	25s
	2m 7s

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