test: experimental runners

What does this MR do and why?

A test MR, not to be merged - testing new experimental runners for the GitLab repo.

References

gitlab-com/gl-infra/production-engineering#27348 (closed)

How to set up and validate locally

1. Push a new commit
2. Change the variable DEFAULT_JOB_TAG in .gitlab-ci.yaml to gitlab-org-experimental.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.