Update _util.py

Author: schloerke

htmltools/_util.py

@@ -90,7 +90,7 @@ def _flatten_recurse(x: Iterable[T | None], result: list[T]) -> None:
 
     for item in x:
         if isinstance(item, TagList):
-            _flatten_recurse(item, result)
+            _flatten_recurse(item.data, result)  # pyright: ignore[reportArgumentType]
         elif isinstance(item, (list, tuple)):
             # Don't yet know how to specify recursive generic types, so we'll tell
             # the type checker to ignore this line.