Fix the MR widget that merged any MR when choosing the option "Merge when pipeline succeeds" from the dropdown

What does this MR do?

Fixes the dropdown option Merge when Pipeline succeeds merging the MR immediately

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

closes #29568 (closed)

cc @stanhu