Update for_helpers.py

Author: BobTheBuidler

mypyc/irbuild/for_helpers.py

@@ -7,7 +7,7 @@
 
 from __future__ import annotations
 
-from typing import Any, Callable, ClassVar
+from typing import Any, Callable, ClassVar, cast
 
 from mypy.nodes import (
     ARG_POS,