agent: Support protection for Kyber keys.

* agent/protect.c (protect_info): Support the Kyber variants.

We used to store the Kyber parts of a dual key unprotected because the
ECC should be enough to protect against a local attackers. But for
policy reasons we of course also need to protect the Kyber secret key
stored on on-disk.

• GnuPG-bug-id: T6638