setup.py: "qml_gui" extra: restrict pyqt to "6.10.x"

I had misunderstood how "~=" works.
Previous meant >=6.10, but any 6.x.
While I actually wanted 6.10.0<=v<6.11.

follow-up 96a3345ab5a3c41c89b4b5bac2d8bde12d753392

ref https://peps.python.org/pep-0440/#compatible-release