fix transient rspec failure due to Poll.js race condition

What does this MR do?

Don't call error callback for aborted poll requests. These are triggered while page unloading, so if navigating to another page is slow a console error is logged.

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

• possibly also worth updating issue_show/components/app.vue to have a better error callback (or remove the error callback). Currently it just logs the error and does nothing.

Why was this MR needed?

fix tests

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 #35225 (closed)