test: add test about unencrypted PKCS#8 private key for RSA

PR-URL: https://github.com/nodejs/node/pull/26898
Refs: https://github.com/nodejs/node/issues/24928


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>