Made assertions in invalid_models_tests consistent.

tests/invalid_models_tests/test_backend_specific.py

@@ -25,6 +25,4 @@ class BackendSpecificChecksTests(SimpleTestCase):
 
         field = Model._meta.get_field('field')
         with mock.patch.object(connections['default'].validation, 'check_field', return_value=[error]):
-            errors = field.check()
-
-        self.assertEqual(errors, [error])
+            self.assertEqual(field.check(), [error])

tests/invalid_models_tests/test_custom_fields.py

@@ -17,5 +17,4 @@ class CustomFieldTest(SimpleTestCase):
             other_field = models.IntegerField()
 
         field = Model._meta.get_field('field')
-        errors = field.check()
-        self.assertEqual(errors, [])
+        self.assertEqual(field.check(), [])