Add stubs for operator.is_none and operator.is_not_none (#12535)

Co-authored-by: Akuli <akuviljanen17@gmail.com>

stdlib/operator.pyi

@@ -61,6 +61,9 @@ __all__ = [
 if sys.version_info >= (3, 11):
     __all__ += ["call"]
 
+if sys.version_info >= (3, 14):
+    __all__ += ["is_none", "is_not_none"]
+
 __lt__ = lt
 __le__ = le
 __eq__ = eq