fix(ui/tree/clone): `is_openend` should not be false

Resolve https://github.com/helix-editor/helix/pull/5768#discussion_r1133066209

helix-term/src/ui/tree.rs

@@ -74,7 +74,7 @@ impl<T: Clone> Clone for Tree<T> {
             item: self.item.clone(),
             index: self.index,
             children: self.children.clone(),
-            is_opened: false,
+            is_opened: self.is_opened,
             parent_index: self.parent_index,
         }
     }