Unhandled error causing infrequent 500s from the sync endpoint

[sentry-io]

Sentry Issue: STUDIO-GCC

TransactionManagementError: An error occurred in the current transaction. You can't execute queries until the end of the 'atomic' block.
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  File "contentcuration/viewsets/sync/endpoint.py", line 153, in post
    response_payload.update(self.handle_changes(request))
  File "contentcuration/viewsets/sync/endpoint.py", line 61, in handle_changes
    apply_channel_changes_task.fetch_or_enqueue(request.user, channel_id=channel_id)
  File "contentcuration/utils/celery/tasks.py", line 275, in fetch_or_enqueue
    return self.enqueue(user, **kwargs)
  File "contentcuration/utils/celery/tasks.py", line 232, in enqueue
    task_result = get_task_model(self, task_id)
  File "contentcuration/utils/celery/tasks.py", line 74, in get_task_model
    return ref.backend.TaskModel.objects.get_task(task_id)