GUISupportQtOpenGL: add to the Qt group

Since QVTKWidget2 lives here, add it to the Qt group.

GUISupport/QtOpenGL/module.cmake

-if(VTK_RENDERING_BACKEND STREQUAL "OpenGL")
-  set(_groups GROUPS Qt)
-endif()
 vtk_module(vtkGUISupportQtOpenGL
-  ${_groups}
+  GROUPS Qt
   DEPENDS
     vtkGUISupportQt
     vtkRendering${VTK_RENDERING_BACKEND}