Update the QA image Dockerfile to include 'config/light_settings.rb'

What does this MR do?

!17711 (merged) modified lib/gitlab.rb to require config/light_settings.rb.

Unfortunately, the QA image broke with this change because it only includes the necessary files and it should have been updated to include config/light_settings.rb as well.

This is what this MR does.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] 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

Closes #33309 (closed).