pkcs5

x509-cert: use `SubjectPublicKeyInfoOwned::from_key` #2613

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	4m 24s
build (1.65.0, wasm32-unknown-unknown)	4m 23s
test (1.65.0)	4m 44s
build (stable, thumbv7em-none-eabi)	41s
build (stable, wasm32-unknown-unknown)	38s
test (stable)	54s
minimal-versions / minimal-versions	1m 0s
	16m 44s

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