Cannot assign to bot users from quick actions

Summary

Recent changes have caused the inability to assign to bot users from quick-actions.

Steps to reproduce

Try to assign to an automated bot (For gitlab-org/gitlab>, an example is @gitlab-release-tools-bot).

Example Project

Happens on all projects, but easily verifiable with gitlab-org/gitlab>

What is the current bug behavior?

User is not found. Error message is displayed.

What is the expected correct behavior?

Bot should be assigned.

Output of checks

This bug happens on GitLab.com

Possible fixes

Change visibility check at https://gitlab.com/gitlab-org/gitlab/blob/master/app/services/quick_actions/interpret_service.rb#L72-89

cc. @phikai