This fixes a regression in #39557--for the project diff, we rely on
getting an event when a path inside a git repository changes, even if
the git state of the repository didn't change as a result (e.g. a new
modification to a file that already had the "modified" status).

I've also changed this code to send the `UpdateRepository` proto message
even when the git state didn't change, since otherwise we have the same
problem in SSH and collab projects.

Release Notes:

- N/A