Add _loop, _tasks, and _on_task_done to the stub for asyncio.TaskGroup (#10612)

stdlib/asyncio/taskgroups.pyi

@@ -1,10 +1,11 @@
 import sys
 from contextvars import Context
 from types import TracebackType
-from typing import TypeVar
+from typing import Any, TypeVar
 from typing_extensions import Self
 
 from . import _CoroutineLike
+from .events import AbstractEventLoop
 from .tasks import Task
 
 if sys.version_info >= (3, 12):
@@ -15,6 +16,10 @@ else:
 _T = TypeVar("_T")
 
 class TaskGroup:
+    _loop: AbstractEventLoop | None
+    _tasks: set[Task[Any]]
+
     async def __aenter__(self) -> Self: ...
     async def __aexit__(self, et: type[BaseException] | None, exc: BaseException | None, tb: TracebackType | None) -> None: ...
     def create_task(self, coro: _CoroutineLike[_T], *, name: str | None = None, context: Context | None = None) -> Task[_T]: ...
+    def _on_task_done(self, task: Task[object]) -> None: ...