Ensure all servers are using post-quantum crypto for SSH connections

We have some servers for which my SSH client display (since quite some time) this kind of message:

```
** WARNING: connection is not using a post-quantum key exchange algorithm.
** This session may be vulnerable to "store now, decrypt later" attacks.
** The server may need to be upgraded. See https://openssh.com/pq.html
```

It is probably not urgent to fix, but important enough to mention and plan for this.