Always check for `__dictrefoffset__` and `__weakoffset__` in `dataclasses` with slots

Bug report

See https://github.com/python/cpython/pull/118099#discussion_r1575244611 and https://github.com/python/cpython/issues/118033

We now correctly check for __dictoffset__ and __weakoffset__ on C types without __slots__ defined: https://github.com/python/cpython/blob/c68acb1384a51eb745f572687eaf677371b9e765/Lib/dataclasses.py#L1201-L1212

But, not in this case: https://github.com/python/cpython/blob/c68acb1384a51eb745f572687eaf677371b9e765/Lib/dataclasses.py#L1213-L1218

So, in theory there might be C types with __slots__ and __dictoffset__ and __weakoffset__.

I will investigate!