hmac: bump `digest` to v0.11.0-pre.8 #287

Job	Run time
build (1.72.0, thumbv7em-none-eabi)	15s
test (1.72.0)	20s
build (1.72.0, wasm32-unknown-unknown)	15s
test (stable)	14s
build (stable, thumbv7em-none-eabi)	20s
build (stable, wasm32-unknown-unknown)	15s
minimal-versions / minimal-versions	28s
	2m 7s

Provide feedback