[stubtest] ignore __conditional_annotations__

[jorenham]

On Python 3.14, this module attribute seems to exist in certain situations:

>>> if True:
...     a: str
...     
>>> __conditional_annotations__
{0}

It's a pretty esoteric attribute without any documentation. It seems to have been added in python/cpython#130935

Either way, stubtest was complaining about it in scipy-stubs. So all things considered, I figured it'd be best to just ignore it.