[Part] ViewProvider.cpp: add include needed for Qt 6

- as reported in #8053, QObject has to be included to be able to compile with Qt 6

src/Mod/Part/Gui/ViewProvider.cpp

@@ -20,9 +20,12 @@
  *                                                                         *
  ***************************************************************************/
 
-
 #include "PreCompiled.h"
 
+#ifndef _PreComp_
+# include <QObject>
+#endif
+
 #include <App/Document.h>
 #include <Base/Console.h>
 #include <Base/Exception.h>