Fix a Ruby 2.4 incompatibility in Ci::CreatePipelineService

What does this MR do?

This fixes a Ruby 2.4 incompatibility in Ci::CreatePipelineService.

What are the relevant issue numbers?

Closes #57426 (closed).

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] 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
• Security reports checked/validated by reviewer