Fix #118395: use copy instead of new for geometry nodes in modifiers list

Now it behaves the same as the materials list UI.

Pull Request: https://projects.blender.org/blender/blender/pulls/118420

source/blender/modifiers/intern/MOD_nodes.cc

@@ -2293,16 +2293,9 @@ static void panel_draw(const bContext *C, Panel *panel)
   uiLayoutSetPropDecorate(layout, false);
 
   if (!(nmd->flag & NODES_MODIFIER_HIDE_DATABLOCK_SELECTOR)) {
-    uiTemplateID(layout,
-                 C,
-                 ptr,
-                 "node_group",
-                 "node.new_geometry_node_group_assign",
-                 nullptr,
-                 nullptr,
-                 0,
-                 false,
-                 nullptr);
+    const char *newop = (nmd->node_group == nullptr) ? "node.new_geometry_node_group_assign" :
+                                                       "object.geometry_node_tree_copy_assign";
+    uiTemplateID(layout, C, ptr, "node_group", newop, nullptr, nullptr, 0, false, nullptr);
   }
 
   if (nmd->node_group != nullptr && nmd->settings.properties != nullptr) {