The flag wxMOD_ALTGR is defined in wxWidgets as wxMOD_CONTROL|wxMOD_ALT
So AltGr key cannot used as modifier key because it is the same as
Alt key + Ctrl key that is already handled.
So the previous code did not work with modifiers Alt key, Ctrl key and Altgr key
Fixes https://gitlab.com/kicad/code/kicad/-/issues/21696