Fix error when using invalid branch name when creating a new pipeline

What does this MR do?

This MR fixes 500 error when creating a new pipeline though user interface ("Run pipeline")

Are there points in the code the reviewer needs to double check?

Is this a good approach to catch those exceptions on Repository level?

Does this MR meet the acceptance criteria?

• Changelog entry added
• Tests
  • Added for this feature/bug

What are the relevant issue numbers?

Closes #23982 (closed)