The PUT /repositories/<n>/ API supports an `archive_name` field which can hide the repository and give it a special name. This was going through the regular repository form to actually handle the save operation, which meant that if the repository being archived was inaccessible for some reason, the operation would fail. This change makes it so we check if the only thing being done is archiving the repository, and if so we skip using the form and just update the model itself. Testing Done: Ran unit tests.