testlists user branches do not update to main, automatically resolving merge conflicts is not trivial

[aagbsn]

when a user submits new URLs to the test-lists service the user's git branch isn't updated to the current main. because merge conflicts do not always resolve automatically, simply merging the upstream main branch into the users branch isn't an easy fix for this problem.

currently, these PR get created and any merge conflicts are left for the reviewer to address, which has caused issues with URLs being removed accidentally.

this issue does support needing a more flexible backend for the test-lists service, e.g. using a database rather than git for the backend.