Ignore Celery task results

Since we don't use the results of our Celery tasks (all of them return
None implicitly), it's prudent to set the ignore_result flag, for a
potential performance improvement. See the Celery docs for details [1].

We could do this with the global CELERY_IGNORE_RESULT setting, but it
offers more flexibility if we want to use task results in the future to
set it on a per-task basis.

[1]: https://docs.celeryq.dev/en/stable/userguide/tasks.html#ignore-results-you-don-t-want

bookwyrm/models/antispam.py

@@ -65,7 +65,7 @@ class AutoMod(AdminModel):
     created_by = models.ForeignKey("User", on_delete=models.PROTECT)
 
 
-@app.task(queue=LOW)
+@app.task(queue=LOW, ignore_result=True)
 def automod_task():
     """Create reports"""
     if not AutoMod.objects.exists():