Intermittent migration test failure on master

[jaredlockhart]

Just ran make check on master@6154a7f25c8c731c13a9faa54dcf6d16afb6d8f2 and got this test failure, ran make check again and it passed:

_______________________________________________________________________ Test0007FilterConversion.test_reverse ________________________________________________________________________

self = <normandy.recipes.tests.test_migrations.Test0007FilterConversion object at 0x7f054a1c4450>
migrations = <normandy.conftest.migrations.<locals>.Migrator object at 0x7f05493da810>

    def test_reverse(self, migrations):
        # Get the pre-migration models
        old_apps = migrations.migrate("recipes", "0007_convert_simple_filters_to_filter_objects")
        Recipe = old_apps.get_model("recipes", "Recipe")
        Action = old_apps.get_model("recipes", "Action")
        RecipeRevision = old_apps.get_model("recipes", "RecipeRevision")
        Channel = old_apps.get_model("recipes", "Channel")
        Country = old_apps.get_model("recipes", "Country")
        Locale = old_apps.get_model("recipes", "Locale")
    
        # Create test data
        recipe = Recipe.objects.create()
        action = Action.objects.create()
        channel1 = Channel.objects.create(slug="beta")
        channel2 = Channel.objects.create(slug="release")
        country1 = Country.objects.create(code="US")
        country2 = Country.objects.create(code="CA")
>       locale1 = Locale.objects.create(code="en-US")

normandy/recipes/tests/test_migrations.py:313: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/opt/venv/lib/python3.7/site-packages/django/db/models/manager.py:82: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
/opt/venv/lib/python3.7/site-packages/django/db/models/query.py:422: in create
    obj.save(force_insert=True, using=self.db)
/opt/venv/lib/python3.7/site-packages/django/db/models/base.py:741: in save
    force_update=force_update, update_fields=update_fields)
/opt/venv/lib/python3.7/site-packages/django/db/models/base.py:790: in save_base
    update_fields=update_fields, raw=raw, using=using,
/opt/venv/lib/python3.7/site-packages/django/dispatch/dispatcher.py:175: in send
    for receiver in self._live_receivers(sender)
/opt/venv/lib/python3.7/site-packages/django/dispatch/dispatcher.py:175: in <listcomp>
    for receiver in self._live_receivers(sender)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

sender = <class '__fake__.Locale'>, instance = <Locale: Locale object (214)>
kwargs = {'created': True, 'raw': False, 'signal': <django.db.models.signals.ModelSignal object at 0x7f05504f8c50>, 'using': 'default'}, update_fields = None

    def reset_state(sender, instance, **kwargs):
        # original state should hold all possible dirty fields to avoid
        # getting a `KeyError` when checking if a field is dirty or not
        update_fields = kwargs.pop('update_fields', {})
>       new_state = instance._as_dict(check_relationship=True)
E       AttributeError: 'Locale' object has no attribute '_as_dict'

/opt/venv/lib/python3.7/site-packages/dirtyfields/dirtyfields.py:136: AttributeError

[mythmon]

This is the same as #2219.