UI: Unify how we detect abort errors

As part of the Ember 3.20 and related dependency upgrades, the existing `error instanceof AbortError` check became insufficient.

With some research, I think we can find a new way to handle this issue with a single conditional.

https://github.com/hashicorp/nomad/blob/4e0e33e7c0bfbf48b4729d3b02950b9ced7edb06/ui/app/adapters/watchable.js#L58-L68

Introduced in #9912

Start with ui/app/adapters/watchable.js at lines 58-68 and review how abort errors are currently detected after the Ember 3.20 and dependency upgrades. Identify a single conditional that handles the affected abort errors, then verify the behavior with the relevant UI tests.

Written by the indexing model from the issue text.