### 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)

if (!can_drop_data_fw(p_point, p_data, p_from)) {
		return;
	}
	bool is_shift = Input::get_singleton()->is_key_pressed(Key::SHIFT);
	bool is_ctrl = Input::get_singleton()->is_key_pressed(Key::CTRL);
	selected_files.clear();
	Dictionary d = p_data;
	if (d.has("type") && String(d["type"]) == "files") {
		selected_files = d["files"];
	}
	List<Node *> selected_nodes = EditorNode::get_singleton()->get_editor_selection()->get_selected_node_list();
	Node *root_node = EditorNode::get_singleton()->get_edited_scene();
	if (selected_nodes.size() == 1) {
		Node *selected_node = selected_nodes[0];
		target_node = root_node;
		if (is_ctrl) {
			target_node = selected_node;
		} else if (is_shift && selected_node != root_node) {
			target_node = selected_node->get_parent();