@set_code_owner_attribute clashes with django-user-tasks

(I'm not sure whether this is an issue with edx-django-utils, with django-user-tasks, or both...)

Adding @set_code_owner_attribute and @shared_task to the same function causes errors when that function is an instance of UserTask.

For this reason, the import_olx and export_olx tasks in edx-platform do not use @set_code_owner_attribute: https://github.com/openedx/edx-platform/blob/db252978f3f315c896b07443f70febdc043faee4/cms/djangoapps/contentstore/tasks.py#L310-L311

I recently (accidentally) confirmed this issue... I was working on update_children_task in the content_libraries djangoapp, and had this:

@shared_task(base=LibraryUpdateChildrenTask, bind=True)
@set_code_owner_attribute
def update_children_task(self, user_id, dest_block_key, version=None):
    ....

The celery task did still work, but logs contained a background exception:

 Traceback (most recent call last):
   File "/openedx/venv/lib/python3.8/site-packages/celery/utils/dispatch/signal.py", line 276, in send
     response = receiver(signal=self, sender=sender, **named)
   File "/openedx/venv/lib/python3.8/site-packages/user_tasks/signals.py", line 215, in start_user_task
     sender.status.start()
   File "/openedx/venv/lib/python3.8/site-packages/user_tasks/tasks.py", line 84, in status
     name = self.generate_name(arguments_dict)
   File "/openedx/edx-platform/openedx/core/djangoapps/content_libraries/tasks.py", line 274, in generate_name
     key = arguments_dict['dest_block_key']
 KeyError: 'dest_block_key'

Digging in, I found that this key is missing because the django-user-tasks-defined function arguments_as_dict was not properly returning a dictionary. The underlying failure seems to be that in the call inspect.getcallargs(cls.run, ...), cls.run does not always actually equal the function defining the celery task (update_children_task), but rather the stub method Task.run. I imagine that this has to do with @set_code_owner_attribute iterfering with the introspection that @shared_task and/or django-user-tasks relies upon.

I am not exactly sure what the react or impact of this bug is. I do know for sure that developers should not use @set_code_owner_attribute on any Django user task function.

Start with the update_children_task example and compare the behavior of @shared_task, @set_code_owner_attribute, and UserTask. Read the referenced django-user-tasks arguments_as_dict implementation and reproduce the background exception, checking whether the task function is preserved during introspection. Done means compatible decorator behavior or a clearly documented limitation, with the missing dest_block_key error resolved.