devel/py-qt6-pyqt: Update to 6.8.1

Support for the QtStateMachine module has been added.

Restrict QtPdf[Widgets] bindings to archs supported by print/qt6-pdf.
These really should be split out into a separate port along with a few
other lesser used bindings, but this is an intermediate step towards
better support for Tier 2 archs.

https://www.riverbankcomputing.com/news/PyQt_v6.8.1_Released

MFH: 2025Q1