Achieve centralizing imports from Ember

[BlueCutOfficial]

Description

#2668 achieved the centralization of all Ember imports in ember_debug code. However, one developer contributing to the inspector could still implement a new import ember from 'utils/ember'. This is not wanted, and we should highlight it by removing this export, since it's no longer used*.

no longer used*: there was one last forgotten reference to the default Ember export in profile-manager-test. It was removed in favor of the named export used by the test

Additionally, this PR:

• Fixes a tiny issue with the runloop introduced in Cleanup import ember #2668. We've been a bit fast removing the whole if block since the fallback mechanics is still there.
• Add a timeout on the GitHub job, because QUnit doesn't timeout correctly. When looking into the no longer used problem above, I had a test stuck for Ember <=3.24, and the CI was on its way to GitHub's default 6-hour timeout.

[mansona]

fantastic 🎉