Fix job_details.json schema

What does this MR do?

Fix job_detail.json schema type should be $ref for runners property.

Add missing required fields

What are the relevant issue numbers?

gitlab-org/gitlab-ce#51927

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #51927 (closed)