add several NamedTuple base classes (#12987)

stdlib/sched.pyi

@@ -1,6 +1,6 @@
 import sys
 from collections.abc import Callable
-from typing import Any, NamedTuple
+from typing import Any, NamedTuple, type_check_only
 from typing_extensions import TypeAlias
 
 __all__ = ["scheduler"]
@@ -17,13 +17,16 @@ if sys.version_info >= (3, 10):
         kwargs: dict[str, Any]
 
 else:
-    class Event(NamedTuple):
+    @type_check_only
+    class _EventBase(NamedTuple):
         time: float
         priority: Any
         action: _ActionCallback
         argument: tuple[Any, ...]
         kwargs: dict[str, Any]
 
+    class Event(_EventBase): ...
+
 class scheduler:
     timefunc: Callable[[], float]
     delayfunc: Callable[[float], object]