test: test with a larger RSA key

OpenSSL 1.1.0 rejects RSA keys smaller than 1024 bits by default. Fix
the tests to use larger ones. This test only cares that the PEM blob be
missing a trailing newline. Certificate adapted from
test/fixtures/cert.pem.

PR-URL: https://github.com/nodejs/node/pull/16130
Backport-PR-URL: https://github.com/nodejs/node/pull/18622


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>