x509-cert: use `SubjectPublicKeyInfoOwned::from_key` (#1271) #1526

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	4m 2s
build (1.65.0, wasm32-unknown-unknown)	3m 59s
build (stable, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	19s
test (1.65.0)	3m 58s
test (stable)	16s
minimal-versions / minimal-versions	29s
	13m 20s

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