Fix #112330: Group sockets not initialized when created by link-drag

The link-drag operator creates the group interface socket, but then did
not initialize the default value.

Pull Request: https://projects.blender.org/blender/blender/pulls/112337

source/blender/editors/space_node/link_drag_search.cc

@@ -93,6 +93,7 @@ static void add_group_input_node_fn(nodes::LinkSearchOpParams &params)
       params.socket.typeinfo->idname,
       NODE_INTERFACE_SOCKET_INPUT,
       nullptr);
+  socket_iface->init_from_socket_instance(&params.socket);
   BKE_ntree_update_tag_interface(&params.node_tree);
 
   bNode &group_input = params.add_node("NodeGroupInput");