Fixed flake8 warning.

tests/model_forms/tests.py

@@ -2383,6 +2383,7 @@ class CustomFieldWithQuerysetButNoLimitChoicesTo(forms.Field):
 
 class StumpJokeWithCustomFieldForm(forms.ModelForm):
     custom = CustomFieldWithQuerysetButNoLimitChoicesTo()
+
     class Meta:
         model = StumpJoke
         fields = ()  # We don't need any fields from the model