gh-108267: Dataclasses docs: Fix object.__setattr__ typo (#108355)

Fixed a sentence in dataclasses.rst

Changed "__setattr__" to "object.__setattr__" in a section that was specifically supposed to refer to the __setattr__ method of the object class. Also suppressed the link to the data model docs for __setattr__, since we're talking about a specific __setattr__ implementation, not __setattr__ methods in general.