Use correct variant type in generic wxDataViewChoiceByIndexRenderer

This solves the same problem as daa8fd03f3 did
for the GTK+ native version and ensures that the variant type at the renderer
level is consistent with the type of the values actually used with this
renderer (which are integers as they are indices).

Closes #17474.

src/common/datavcmn.cpp

@@ -1778,6 +1778,7 @@ wxDataViewChoiceByIndexRenderer::wxDataViewChoiceByIndexRenderer( const wxArrayS
                                   wxDataViewCellMode mode, int alignment ) :
       wxDataViewChoiceRenderer( choices, mode, alignment )
 {
+    m_variantType = wxS("long");
 }
 
 wxWindow* wxDataViewChoiceByIndexRenderer::CreateEditorCtrl( wxWindow *parent, wxRect labelRect, const wxVariant &value )