Fix job scheduling when extra CI minutes purchased

What does this MR do?

This MR fixes bug with the job scheduling not returning a job if the customer had purchased extra CI minutes. The bug occurred when the namespace inherited application-wide Runner minutes limit. In that case we were only considering the application limit without adding the extra CI minutes purchased. If the user had used more than the application-wide minutes it would result in jobs never being picked up by the Runners.

Reference: https://gitlab.com/gitlab-org/gitlab-ce/issues/64987

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