cubicweb-worker #4117297 fix API blunder [not validated]

There is a confusion in the WorkerAdapter: it should be is_instance('CWWorkerTask') and the worker dispatcher should adapt the operation from the task.

Leniency of the base selector allowed the current situation to somewhat work.

The fix should not affect existing users.

priorityimportant
typebug
done in3.0.2
load0.200
load left0.000
closed by#fa1ae48776f5 [entities] fix adapter definition: it should be a Task adapter
patch[entities] fix adapter definition: it should be a Task adapter [applied]
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