fix skip_replace hack docs

[decorator-factory]

I was recently pointed to the fact that the typing documentation does in fact demand that dataclass_transforms support __replace__:

https://typing.python.org/en/latest/spec/dataclasses.html#the-dataclass-transform-decorator

Except where stated otherwise, classes impacted by dataclass_transform, either by inheriting from a class that is decorated with dataclass_transform or by being decorated with a function decorated with dataclass_transform, are assumed to behave like stdlib dataclass().

So the documentation I wrote was wrong: type checkers are supposed to assume that the dataclass_transform produces classes with __replace__ support in 3.13+.