Set role to data when creating an Optional from | None

[hoodmane]

This is not super important, but when converting | None to Optional the code sets the role incorrectly to class and so generates dead links.

[gaborbernat]

Please add tests 👍 I think is data only on 3.11 not 3.10.

[hoodmane]

It's also a data in Python 3.10 -- note that Optional is in _PYDATA_ANNOTATIONS so if an Optional is generated directly instead of via a conversion from A | None then it will get :py:data:. So the test can just ask for e.g., Union[str, None] and Optional[str] to produce the same output.