Add missing argument in proxy style init

[albsod]

This adds PyQt v6.5 compatibility by fixing this error:

TypeError: arguments did not match any overloaded call:
QProxyStyle(style: typing.Optional[QStyle] = None): not enough arguments
QProxyStyle(key: Optional[str]): not enough arguments

poetry run pytest tests
pytest-xvfb could not find Xvfb. You can install it to prevent windows from being shown.
=============================================================================================== test session starts ===============================================================================================
platform linux -- Python 3.11.2, pytest-7.2.0, pluggy-1.0.0
Using --randomly-seed=4040543564
PyQt6 6.5.2 -- Qt runtime 6.5.1 -- Qt compiled 6.5.2
rootdir: /home/albin/projekt/host-mobility/PyQtDarkTheme
plugins: anyio-3.6.2, xvfb-2.0.0, randomly-3.12.0, mock-3.10.0, qt-4.2.0, cov-4.0.0
collected 157 items                                                                                                                                                                                               

tests/test_color.py ..................................................................                                                                                                                      [ 42%]
tests/test_qdarktheme.py ...........................                                                                                                                                                        [ 59%]
tests/test_svg.py .....                                                                                                                                                                                     [ 62%]
tests/test_filters.py ....................                                                                                                                                                                  [ 75%]
tests/test_template_engine.py ...........                                                                                                                                                                   [ 82%]
tests/test_qdarktheme_with_qt.py ......................                                                                                                                                                     [ 96%]
tests/test_widget_gallery.py .                                                                                                                                                                              [ 96%]
tests/test_util.py .....                                                                                                                                                                                    [100%]

=============================================================================================== 157 passed in 1.96s ===============================================================================================