Don't use an RSA-PSS cert for RSA key exchange

If we have selected a ciphersuite using RSA key exchange then we must
not attempt to use an RSA-PSS cert for that.

Fixes #7059

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7099)