### 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)

}
		} else if (m->get_button_mask().has_flag(MouseButtonMask::MIDDLE)) {
			const Key mod = _get_key_modifier(m);
			if (nav_scheme == NAVIGATION_GODOT) {
				if (mod == _get_key_modifier_setting("editors/3d/navigation/pan_modifier")) {
					nav_mode = NAVIGATION_PAN;
				} else if (mod == _get_key_modifier_setting("editors/3d/navigation/zoom_modifier")) {
					nav_mode = NAVIGATION_ZOOM;
				} else if (mod == Key::ALT || mod == _get_key_modifier_setting("editors/3d/navigation/orbit_modifier")) {
					
					nav_mode = NAVIGATION_ORBIT;
				}
			} else if (nav_scheme == NAVIGATION_MAYA) {
				if (mod == _get_key_modifier_setting("editors/3d/navigation/pan_modifier")) {
					nav_mode = NAVIGATION_PAN;
				}
			}
		} else if (EDITOR_GET("editors/3d/navigation/emulate_3_button_mouse")) {
			
			const Key mod = _get_key_modifier(m);
			if (mod != Key::NONE) {
				if (mod == _get_key_modifier_setting("editors/3d/navigation/pan_modifier")) {
					nav_mode = NAVIGATION_PAN;
				} else if (mod == _get_key_modifier_setting("editors/3d/navigation/zoom_modifier")) {
					nav_mode = NAVIGATION_ZOOM;
				} else if (mod == Key::ALT || mod == _get_key_modifier_setting("editors/3d/navigation/orbit_modifier")) {
					
					nav_mode = NAVIGATION_ORBIT;
				}
			}