### 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 (nav_mode == Node3DEditorViewport::NAVIGATION_NONE) {
		return;
	}
	Vector2 center = get_size() / 2.0;
	float radius = get_size().x / 2.0;
	const bool focused = focused_index != -1;
	draw_circle(center, radius, Color(0.5, 0.5, 0.5, focused || hovered ? 0.35 : 0.15));
	const Color c = focused ? Color(0.9, 0.9, 0.9, 0.9) : Color(0.5, 0.5, 0.5, 0.25);
	Vector2 circle_pos = focused ? center.move_toward(focused_pos, radius) : center;
	draw_circle(circle_pos, AXIS_CIRCLE_RADIUS, c);
	draw_circle(circle_pos, AXIS_CIRCLE_RADIUS * 0.8, c.darkened(0.4));
}
void ViewportNavigationControl::_process_click(int p_index, Vector2 p_position, bool p_pressed) {