[Catalog] Fix issue with ListPopupWindow a11y

PiperOrigin-RevId: 683696939

Author: imhappi

catalog/java/io/material/catalog/menu/MenuMainDemoFragment.java

@@ -181,6 +181,7 @@ private ListPopupWindow initializeListPopupMenu(View v) {
             getResources().getStringArray(R.array.cat_list_popup_window_content));
     listPopupWindow.setAdapter(adapter);
     listPopupWindow.setAnchorView(v);
+    listPopupWindow.setModal(true);
     listPopupWindow.setOnItemClickListener(
         (parent, view, position, id) -> {
           Snackbar.make(