Type and mark as final module-level dunders not meant to be overwritten in stdlib/ (#9709)

stdlib/heapq.pyi

@@ -2,12 +2,13 @@ from _heapq import *
 from _typeshed import SupportsRichComparison
 from collections.abc import Callable, Iterable
 from typing import Any, TypeVar
+from typing_extensions import Final
 
 __all__ = ["heappush", "heappop", "heapify", "heapreplace", "merge", "nlargest", "nsmallest", "heappushpop"]
 
 _S = TypeVar("_S")
 
-__about__: str
+__about__: Final[str]
 
 def merge(
     *iterables: Iterable[_S], key: Callable[[_S], SupportsRichComparison] | None = None, reverse: bool = False