fix: we do care about the order of Union fields

See lovasoa#246 (comment)

tests/test_field_for_schema.py

@@ -76,17 +76,10 @@ def _assertAttrsEqual(self, a, b, msg=None):
                 # TestCase.assertSequenceEqual tests item equality with __eq__.
                 # (It doesn't dispatch to an assert* method based on the item type.)
                 # So we'll do the comparison ourself using assertEqual.
-
-                if type(a).__name__ == "Union" and attr == "union_fields":
-                    # We don't care about the order of the union fields.
-                    # Sort before comparing.
-                    value_a = sorted(value_a, key=repr)
-                    value_b = sorted(value_b, key=repr)
-
                 for v1, v2 in zip(value_a, value_b):
                     self.assertEqual(v1, v2, msg)
             else:
-                self.assertEqual(value_a, value_b)
+                self.assertEqual(value_a, value_b, msg)
 
     def test_int(self):
         self.assertFieldsEqual(