### 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)

Node3DEditorViewport *current_viewport = Object::cast_to<Node3DEditorViewport>(p_viewport);
	if (!current_viewport) {
		return;
	}
	EditorDebuggerNode *const debugger = EditorDebuggerNode::get_singleton();
	camera_override_viewport_id = current_viewport->index;
	if (debugger->get_camera_override() >= EditorDebuggerNode::OVERRIDE_3D_1) {
		using Override = EditorDebuggerNode::CameraOverride;
		debugger->set_camera_override((Override)(Override::OVERRIDE_3D_1 + camera_override_viewport_id));
	}
}
void Node3DEditor::_menu_item_pressed(int p_option) {
	EditorUndoRedoManager *undo_redo = EditorUndoRedoManager::get_singleton();
	switch (p_option) {
		case MENU_TOOL_SELECT:
		case MENU_TOOL_MOVE:
		case MENU_TOOL_ROTATE:
		case MENU_TOOL_SCALE:
		case MENU_TOOL_LIST_SELECT: {
			for (int i = 0; i < TOOL_MAX; i++) {