While saving favourite templates using api.php?action=options an error might be returned.
- User might already have the max number of templates (QA note: can be tested more easily with e.g. $wgTemplateDataMaxFavorites = 5).
- Backend API might be down for some unspecified reason (e.g. $wgReadOnly).
- The user might've been logged out.
Handle the error and inform the user via bubble notification similar to T377466: Show bubble notification after adding favourite

