tls: re-define max supported version as 1.2

Several secureProtocol strings allow any supported TLS version as the
maximum, but our maximum supported protocol version is TLSv1.2 even if
someone configures a build against an OpenSSL that supports TLSv1.3.

Fixes: https://github.com/nodejs/node/issues/24658

PR-URL: https://github.com/nodejs/node/pull/25024


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>