R1:99c6b53ab224

Explicitly update the repository URI index after making a URI edit

Summary:
Fixes T11936. After editing a repository URI, we were not correctly updating the URI index.

Any other edit to the repository //would// update the index, and this index is only really used by `arc` to figure out which repository a working copy belongs to, so that's how this evaded detection for this long. In particular, creating a repository would usually have an edit after any URI edits, to activate it, which would build the…