minor fix to keep newer mypy happy

Author: eli-bl

openapi_python_client/parser/properties/union.py

@@ -152,9 +152,10 @@ def process_items(
             not isinstance(sub_properties, PropertyError)
             and len([p for p in sub_properties if isinstance(p, HasNamedClass)]) == 1
         ):
+            already_processed_props = sub_properties
 
             def _use_same_name_as_parent_for_that_one_variant(index: int) -> str:
-                for i, p in enumerate(sub_properties):
+                for i, p in enumerate(already_processed_props):
                     if i == index and isinstance(p, HasNamedClass):
                         return name
                 return _add_index_suffix_to_variant_names(index)