Breaks moodle/site:accessallgroups capability

[TimEllis]

Describe the bug
When a staff member does not have the moodle/site:accessallgroups capability, this report still shows all students in the assignment even if the member is not in the student's group.

To Reproduce
Steps to reproduce the behavior:

1. Create course with a staff role without moodle/site:accessallgroups access
2. Add some students and separate them into two groups and add to a grouping
3. Add the staff member to one of the groups
4. Create an assignment in separate groups mode using the created grouping
5. Define a rubric and assign to the assignment
6. Grade all students from both groups
7. login as the staff member and open the Rubric Breakdown report

Expected behavior
Only the students in the group visible to the staff member should show but instead all groups are shown.

[marcusgreen]

Many thanks for the feedback Tim (especially the detail of the exact capability). I will investigate.