sha2: provide support for `spki::AlgorithmIdentifier` #988

Job	Run time
minimal-versions / minimal-versions	37s
set-msrv / set-msrv	5s
test (1.71.0)	32s
build (1.71.0, thumbv7em-none-eabi)	28s
test (stable)	20s
build (1.71.0, wasm32-unknown-unknown)	27s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	16s
	3m 4s

Provide feedback