Revert comment removal

Author: YuriiMotov

sqlmodel/main.py

@@ -747,7 +747,7 @@ def get_column_from_field(field: Any) -> Column:  # type: ignore
             ondelete = getattr(field_info, "ondelete", Undefined)
             if ondelete is Undefined:
                 ondelete = None
-            assert isinstance(ondelete, (str, type(None)))
+            assert isinstance(ondelete, (str, type(None)))  # for typing
             args.append(ForeignKey(foreign_key, ondelete=ondelete))
         else:
             assert isinstance(foreign_key, ForeignKey)