fix Warning

qt6-after/qt6-migrated-legatus/Z/src/QtSingleApplication/qtsingleapplication.cpp

@@ -25,6 +25,9 @@ QtSingleApplication::QtSingleApplication(int &argc, char **argv, bool GUIenabled
     : QCoreApplication(argc, argv)
 #endif
 {
+#ifndef QT6_GUI_AVAILABLE
+    Q_UNUSED(GUIenabled);
+#endif
     sysInit();
 }