Update stubs to pyside6

[chadrik]

Nice work on the latest release!

Now that PySide6 is the reference implementation, the stubs should be updated to PySide6: https://pypi.org/project/types-PySide6/

As with types-PySide2, these stubs are much more accurate than those distributed with PySide6.

[MHendricks]

I was wondering about what needed done with type stubs but I haven't really dealt with them much yet and don't really know how to test that they are working as expected. We may also need to add type def info into Qt.py now that its py3.7+. Are there ways to test the typedefs via gitlab actions?

Is this the source code for types-PySide6? It was hard to find without a link on pypi. https://github.com/LumaPictures/cg-stubs/tree/master/pyside6