pkcs8

x509-cert: use `SubjectPublicKeyInfoOwned::from_key` #2681

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	4m 32s
test (1.65.0)	8m 8s
build (1.65.0, wasm32-unknown-unknown)	4m 39s
test (stable)	3m 21s
build (stable, thumbv7em-none-eabi)	44s
build (stable, wasm32-unknown-unknown)	45s
minimal-versions / minimal-versions	2m 56s
	25m 5s

Provide feedback