Change file extension of `_pillar/known_hosts_salt_ssh.sls` to `.py`

[myii]

@alxwr @aboe76 While introducing salt-lint to this repo, I came across this violation regarding this file:

Examining _pillar/known_hosts_salt_ssh.sls of type state
[206] Jinja variables should have spaces before and after: {{ var_name }}
_pillar/known_hosts_salt_ssh.sls:112
    return {'openssh': {'known_hosts': {'salt_ssh': config}}}

While it's easy to ignore this from a salt-lint perspective, shouldn't this Python file be given the appropriate file extension?