Quiz: Remove groupmembersonly check on override page

0. Enable the experimental setting 'groupmembersonly'. 1. You will need a test course - if you don't have one, create a course with default settings. 2. You will need a test user in the course who does NOT belong to any groups. If you don't already have one, enrol a user. 3. Add a quiz to the test course with default settings. (You don't need to add any questions.) 4. Go to the 'User overrides' screen from the navigation menu inside the quiz. EXPECTED: There should be an 'Add user override' button 5. Click the button EXPECTED: The list of users in the resulting form should include your test user. 6. Edit quiz settings and turn on the 'group members only' option. 7. Go back to quiz overrides page. EXPECTED: The button should be present as before. 8. Click the button. EXPECTED: The list of users should be unchanged. (In other words, the result is the same as if you didn't turn on groupmembersonly.)