Finalize conversion for FKs targeting p_ci_builds - 2 self-managed

What does this MR do and why?

Related to #414396 (closed)

Completes the FK swap for ci_job_artifacts, ci_running_builds and ci_job_variables for self-managed by reintroducing the migrations from !124186 (merged) without the should_run? guards.

⚠ It depends on !124186 (merged) being successfully executed in production.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.