Resolve "Can merge branch before build is started"

What does this MR do?

What are the relevant issue numbers?

Closes #28682 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• N/A Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• N/A Conforms to the database guides
• N/A Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.