Test Architecture Tweak

As I was starting to write tests for sync-fork, wanted to try and simplify the test architecture a little bit.
Tests now update the remote with a second repository instead of using local and resetting.
This was just easier for me to think about and more closely mirrors reality.

@kevgo what do you think?

Note: I used git-extract to pull this off my sync-fork branch.
I'd prefer it if there are multiple branches that the spec defines exactly which branch to use. Defaulting to main seems an invitation for unexpected side effects.