Geometry Nodes: Show node group in modifier UI after duplication

When duplicating the node group from the geometry node editor, show the
data-block selector in the modifier interface. Otherwise it's not clear
that the modifier is using a local data-block, not the original asset.

source/blender/editors/object/object_modifier.cc

@@ -3688,6 +3688,8 @@ static int geometry_node_tree_copy_assign_exec(bContext *C, wmOperator * /*op*/)
   bNodeTree *new_tree = (bNodeTree *)BKE_id_copy_ex(
       bmain, &tree->id, nullptr, LIB_ID_COPY_ACTIONS | LIB_ID_COPY_DEFAULT);
 
+  nmd->flag &= ~NODES_MODIFIER_HIDE_DATABLOCK_SELECTOR;
+
   if (new_tree == nullptr) {
     return OPERATOR_CANCELLED;
   }