Add mlkem768x25519-sha256 from 9.9+

Add `mlkem768x25519-sha256` from 9.9 per https://www.openssh.org/pq.html

Author: kravietz

roles/ssh_hardening/vars/main.yml

@@ -52,3 +52,9 @@ ssh_kex_85_default:
   - sntrup761x25519-sha512@openssh.com
   - curve25519-sha256@libssh.org
   - diffie-hellman-group-exchange-sha256
+
+ssh_kex_99_default:
+  - mlkem768x25519-sha256
+  - sntrup761x25519-sha512@openssh.com
+  - curve25519-sha256@libssh.org
+  - diffie-hellman-group-exchange-sha256