Don't activate items on Ctrl-M in generic wxListCtrl

This is unexpected, so add the check for the modifiers, as is done in
generic wxDataViewCtrl, to only accept the "real" Enter here and not
Ctrl-M sending the same key code.

Closes #17458.

src/generic/listctrl.cpp

@@ -2994,6 +2994,12 @@ void wxListMainWindow::OnChar( wxKeyEvent &event )
 
         case WXK_RETURN:
         case WXK_EXECUTE:
+            if ( event.HasModifiers() )
+            {
+                event.Skip();
+                break;
+            }
+
             SendNotify( m_current, wxEVT_LIST_ITEM_ACTIVATED );
             break;