馃崚 Use QEvent::ApplicationPaletteChanged instead of QEvent::PaletteChanged
When porting to Qt6 in 7e4ef7d7 an event filter was added for qApp for event QEvent::PaletteChanged. However, Qt6 does not actually emit this event for qApp. The correct event is QEvent::ApplicationPaletteChanged.
See https://doc.qt.io/qt-6/qguiapplication-obsolete.html#paletteChanged
(cherry picked from commit 232ff8ac)