### 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 (p_state.has("position")) {
		cursor.pos = p_state["position"];
	}
	if (p_state.has("x_rotation")) {
		cursor.x_rot = p_state["x_rotation"];
	}
	if (p_state.has("y_rotation")) {
		cursor.y_rot = p_state["y_rotation"];
	}
	if (p_state.has("distance")) {
		cursor.distance = p_state["distance"];
	}
	if (p_state.has("orthogonal")) {
		bool orth = p_state["orthogonal"];
		_menu_option(orth ? VIEW_ORTHOGONAL : VIEW_PERSPECTIVE);
	}
	if (p_state.has("view_type")) {
		view_type = ViewType(p_state["view_type"].operator int());
		_update_name();
	}