Mark asyncio.Runner as final (#9353)

As per https://github.com/python/cpython/blob/71b032635d757348cb915c2e8d99392f5bbcb059/Lib/asyncio/runners.py#L47

stdlib/asyncio/runners.pyi

@@ -3,6 +3,7 @@ from _typeshed import Self
 from collections.abc import Callable, Coroutine
 from contextvars import Context
 from typing import Any, TypeVar
+from typing_extensions import final
 
 from .events import AbstractEventLoop
 
@@ -13,6 +14,7 @@ else:
 _T = TypeVar("_T")
 
 if sys.version_info >= (3, 11):
+    @final
     class Runner:
         def __init__(self, *, debug: bool | None = ..., loop_factory: Callable[[], AbstractEventLoop] | None = ...) -> None: ...
         def __enter__(self: Self) -> Self: ...