Fix transient job failures relating to "unhandled Promise rejection" in issue boards

What does this MR do?

Adds proper error handling to failed AJAX requests

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

all tests should pass

Why was this MR needed?

Changes in !9846 (merged) now block AJAX requests generated by javascript after an RSpec test is completed waiting for already-pending requests to finish, it would catch the errors these failing requests where they previously would have been ignored.

Screenshots (if relevant)

n/a

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• [ ] 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 #32030 (closed)