Add order_by tests for Pipelines API

What does this MR do?

This adds test coverage for the order_by option of the "list project pipelines" API endpoint. This test coverage is modeled after the test coverage for Deployments. This MR was motivated by a comment on a related MR.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content