### 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 (_edit.mode == TRANSFORM_NONE && b->is_pressed()) {
					if (b->is_alt_pressed()) {
						if (nav_scheme == NAVIGATION_MAYA) {
							break;
						}
						_list_select(b);
						return;
					}
				}
				if (_edit.mode != TRANSFORM_NONE && b->is_pressed()) {
					cancel_transform();
					break;
				}
				if (b->is_pressed()) {
					const Key mod = _get_key_modifier(b);
					if (!orthogonal) {
						if (mod == _get_key_modifier_setting("editors/3d/freelook/freelook_activation_modifier")) {
							set_freelook_active(true);
						}
					}
				} else {
					set_freelook_active(false);
				}
				if (freelook_active && !surface->has_focus()) {
					
					
					surface->grab_focus();
				}
			} break;
			case MouseButton::MIDDLE: {