Fix test_update_via_tags

Author: Fantomas42

tagging/tests/tests.py

@@ -996,6 +996,7 @@ def test_tag_field_in_modelform(self):
         class TestForm(forms.ModelForm):
             class Meta:
                 model = FormTest
+                fields = forms.ALL_FIELDS
 
         form = TestForm()
         self.assertEqual(form.fields['tags'].__class__.__name__, 'TagField')