Fix broken merge request widget spec

What does this MR do?

Converts the invalid es6 syntax of the merge_request_widget_spec which is actually causing the spec not to run through teaspoon

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

None

Why was this MR needed?

Get specs working again

Screenshots (if relevant)

None

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• 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 #24673 (closed)