[iris] Terminate workers w/ "No accelerator found" errors

[eric-czech]

refs: Discord

This error (No accelerator found) should escalate to terminating the worker (thread):

Here is another instance of this I hit on a different day (from here):

[rjpower]

The underlying basis appears to be a scheduling bug with (sigh, again) reservations. PR incoming

[rjpower]

Should be fixed by the new health tracker.