it: test explicit sync

src/it/test_transport.rs

@@ -63,6 +63,7 @@ impl TestTransport {
             foreign_toplevel_list: Default::default(),
             data_device_manager: Default::default(),
             cursor_shape_manager: Default::default(),
+            syncobj_manager: Default::default(),
             seats: Default::default(),
         });
         self.send(wl_display::GetRegistry {