test: use stronger curves for keygen

This commit updates the named curves P-192 (prime192v1), and secp192k1
to 256 bit versions.

The motivation for this is that in Red Hat Enterprise Linux (RHEL) all
ECC curves < 224 bits are removed from OpenSSL provided by the system.
I'm not sure if other distributions do this but these 256 bit curves are
availalbe in OpenSSL 1.1.0j (current version on master) and OpenSSL
1.1.1 so as far as I can tell it should be safe change to make.

PR-URL: https://github.com/nodejs/node/pull/25564


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>