Disable ZMQ thread authenticator logging

[MetRonnie]

Enough of this:

---

Note

If there is a good reason to turn this back on, we should probably only do it as a child logger: #7423

---

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• No dependency changes
• Tests are not needed
• Changelog entry not needed as minor change
• Docs not needed
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

We might not want to turn logging off completely. E.g, - #7425

These one second interval log entries suggest cylc tui was involved. I think there is already some logic for suppressing Tui sessions in the logs (inherited from cylc monitor), perhaps this needs to be extended?

[MetRonnie]

Nothing in #7425 is suggestive of the ZMQ thread authenticator being an issue? Despite (debug) logging being turned on for the thread authenticator, we didn't see any useful log messages from it