fix readonly __args__

Author: avlonder

dacite/generics.py

@@ -56,10 +56,12 @@ def __concretize(
     hint_origin = get_origin(hint)
     hint_args = get_args(hint)
     if hint_origin and hint_args and hint_origin is not Literal:
-        concretized = tuple(__concretize(a, generics, data_class) for a in hint_args)
-        if concretized != hint_args:
+        concrete_hint_args = tuple(__concretize(a, generics, data_class) for a in hint_args)
+        if concrete_hint_args != hint_args:
+            if sys.version_info.minor >= 9:
+                return hint_origin[concrete_hint_args]
             try:
-                hint.__args__ = concretized
+                hint.__args__ = concrete_hint_args
             except AttributeError as err:
                 raise DaciteError(f"Could not set __args__ on {hint} [original error: {err}]") from None