Add `@gl-quality` as `/qa/` codeowner

What does this MR do?

This adds @gl-quality as code owners for the /qa/ folder.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Availability and Testing

I think we can only see if this works once the file is updated in master.

Closes https://gitlab.com/gitlab-org/quality/team-tasks/issues/369.