Fix some qt6 compile error

cuttlefish/src/colorschemes.h

@@ -7,11 +7,10 @@
 #ifndef CUTTLEFISHCOLORSCHEMES_H
 #define CUTTLEFISHCOLORSCHEMES_H
 
+#include <QAbstractItemModel>
 #include <QObject>
 #include <QString>
 
-class QAbstractItemModel;
-
 class KColorSchemeManager;
 
 namespace CuttleFish

cuttlefish/src/main.cpp

@@ -122,6 +122,8 @@ int main(int argc, char **argv)
 
     qmlRegisterAnonymousType<CuttleFish::IconModel>("org.kde.plasma.sdk", 1);
     qmlRegisterAnonymousType<CuttleFish::ColorSchemes>("org.kde.plasma.sdk", 1);
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     app.setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
     return app.exec();
 }

engineexplorer/ktreeviewsearchline.cpp

@@ -9,6 +9,7 @@
 
 #include "ktreeviewsearchline.h"
 
+#include <QActionGroup>
 #include <QApplication>
 #include <QContextMenuEvent>
 #include <QHBoxLayout>