Fix bug using allow_host_key_change in SSHHook

[a246530]

Incorrect logic for self.allow_host_key_change warning regarding "Remote Identification Change is not verified". This was identified in #9510

closes: #9510

[boring-cyborg]

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[potiuk]

I think it is only half of the solution. The way it will work after the change is that warning is correct, but the behaviour will not be correct. If "allow_host_key_change" will be set to 'False` (default) it will skip completely already present host keys, instead it will treat all the connections as new. This is very bad.

I think this should be solved better:

1. load_system_host_keys should be called in "else" (so skip it wen "allow_host_key_change" is True:
2. there should be a policy to accept all new host keys added when "allow_host_key_change" is True.

This is precisely as described here:

https://stackoverflow.com/questions/47438468/automatically-updating-known-hosts-file-when-host-key-changes-using-paramiko

[eladkal]

Fixed in #24116