Update Code-Quality.gitlab-ci.yml to use `only.refs`

What does this MR do?

I noticed while working on https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15761 that it's impossible to override the only attribute of the code_quality job template because it's using the basic only/except syntax, which takes precedence over the advanced syntax, making it impossible to override the default [tag, branches] to something more advanced.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers