### Godot version

Master (4.2)

### System information

Windows 11 - Vulkan - Nvidia RTX 4070 - intel i5 13600KF

### Issue description

As you can see in the video when you try to add multiple scenes in to the 3D viewport (only with multiple scenes) the editor throws this error.

```
ERROR: Can't add child '@Node3D@18837' to '@SubViewport@9274', already has a parent '@SubViewport@9274'.
   at: (scene\main\node.cpp:1411)
```


Video: https://youtu.be/BVcCIigQJDw

This happens in the latest master (pulled on 2.11.2023).

### Steps to reproduce

Drag couple of the 3d mesh scenes into the 3D viewport and then select multiple scenes and drag them over and observer the error.

### Minimal reproduction project

[TestSceneDragAndDrop.zip](https://github.com/godotengine/godot/files/13253741/TestSceneDragAndDrop.zip)

Node *node = Object::cast_to<Node3D>(ObjectDB::get_instance(clicked));
	Node3D *selected = Object::cast_to<Node3D>(node);
	clicked = ObjectID();
	if (!selected) {
		return;
	}
	if (!p_allow_locked) {
		
		while (node && node != EditorNode::get_singleton()->get_edited_scene()->get_parent()) {
			Node3D *selected_tmp = Object::cast_to<Node3D>(node);
			if (selected_tmp && node->has_meta("_edit_group_")) {
				selected = selected_tmp;
			}
			node = node->get_parent();
		}
	}
	if (p_allow_locked || !_is_node_locked(selected)) {
		if (clicked_wants_append) {
			if (editor_selection->is_selected(selected)) {
				editor_selection->remove_node(selected);
			} else {
				editor_selection->add_node(selected);
			}
		} else {
			if (!editor_selection->is_selected(selected)) {
				editor_selection->clear();