New `qa:selectors-foss` job to run `qa:selectors` as FOSS

What does this MR do?

This adds a new qa:selectors-foss job is the same as qa:selectors but in a simulated FOSS environment.

• qa:selectors: https://gitlab.com/gitlab-org/gitlab/-/jobs/317171803
• qa:selectors-foss: https://gitlab.com/gitlab-org/gitlab/-/jobs/317171832

Related to #32727 (closed).

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