Add tests for PyQt5

Now, only pyside2 is tested.

Either one removes pyside2 from the dependencies, see #144 (closed), or one also install pyqt5 and check with qtpy which one will be used by default.

Probably a separate pipeline is required.

Also, it would make sense to start testing with pyqt6 and pyside6 although set those as optional as they probably will not pass yet.