Ensure that itest repositories are removed

[justinharringa]

Is your feature request related to a problem? Please describe. Currently itest repositories lay around in https://github.com/dockerfile-image-update-itest

Describe the solution you'd like We could potentially have a nightly and/or manually triggerable workflow to blow away any leftover repos in https://github.com/dockerfile-image-update-itest

Describe alternatives you've considered Could do this as part of the code but then there are race conditions.

Additional context N/A