update comments about TypeForm since it has been deferred to python 3.15 (#687)

see https://peps.python.org/pep-0747/

Author: DetachHead

src/typing_extensions.py

@@ -2291,10 +2291,10 @@ def f(val: Union[int, Awaitable[int]]) -> int:
         return typing._GenericAlias(self, (item,))
 
 
-# 3.14+?
+# 3.15+?
 if hasattr(typing, 'TypeForm'):
     TypeForm = typing.TypeForm
-# <=3.13
+# <=3.14
 else:
     class _TypeFormForm(_ExtensionsSpecialForm, _root=True):
         # TypeForm(X) is equivalent to X but indicates to the type checker