[Pkg-utopia-maintainers] Bug#1124673: firewall-applet: Use Qt6

[Bastian Germann]

The mentioned upstream issue already applies on the pyqt5-dependent
firewall-applet package that is in Debian (for wayland). So an update
to pyqt6 does not regress. Please make the update happen. I could provide
a patch but it is trivial to rename the
Depends: python3-pyqt5, python3-dbus.mainloop.pyqt5
to
Depends: python3-pyqt6, python3-dbus.mainloop.pyqt6