From MDL-65129

1. Allow guest access to a course with the forums.
2. Log in as a user that's not enrolled in the course
3. Go to the forum
4. You'll notice that the user can star/unstar discussions
5. Go to the search form
6. The "Search starred discussions only" checkbox is not being shown.
   I'm not sure whether unenrolled users accessing the course via guest access should be able to star/unstar discussions, so we might need to look into this and make the behaviours consistent. So we either
   • hide the star/unstar feature when viewing as an authenticated user; or
   • allow the authenticated, but not enrolled user to search starred discussions only as well