Updated Webmin packages in TurnKey testing repository

[Update: 2020-11-06] Updated Webmin packages which include Webmin v1.960; plus a tweak to the MySQL module.

I'm happy to announce new Webmin packages are available in the TurnKey buster-testing repository. Whilst we have done some testing and they should work fine, I'd really love to have some other testers install them and report back! :)