Make job script a required configuration entry

## What does this MR do?

This MR makes a job script a required configuration entry.

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

## What are the relevant issue numbers?

Closes #24575

See merge request !7566