### 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_scheme == NAVIGATION_GODOT) {
			const Key mod = _get_key_modifier(pan_gesture);
			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 (pan_gesture->is_alt_pressed()) {
				nav_mode = NAVIGATION_PAN;
			}
		}
		switch (nav_mode) {
			case NAVIGATION_PAN: {
				_nav_pan(pan_gesture, -pan_gesture->get_delta());
			} break;
			case NAVIGATION_ZOOM: {
				_nav_zoom(pan_gesture, pan_gesture->get_delta());
			} break;
			case NAVIGATION_ORBIT: {
				_nav_orbit(pan_gesture, -pan_gesture->get_delta());
			} break;
			case NAVIGATION_LOOK: {
				_nav_look(pan_gesture, pan_gesture->get_delta());
			} break;
			default: {
			}