Any public group can be added to merge request approval

Summary

It is possible to use any group you have read access to for merge request approvals.

Steps to reproduce

1. Create a merge request in a project in your personal namespace
2. Add a public group from the instance as an approver

What is the current bug behavior?

Any public group can be selected

What is the expected correct behavior?

Revert to previous behavior.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com