### 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 (key == Key::ENTER || key == Key::KP_ENTER || key == Key::SPACE) {
				commit_transform();
			} else {
				processed = false;
			}
			if (processed) {
				
				set_process_input(false);
				accept_event();
				return;
			}
		}
		if (EDITOR_GET("editors/3d/navigation/emulate_numpad")) {
			const Key code = k->get_physical_keycode();
			if (code >= Key::KEY_0 && code <= Key::KEY_9) {
				k->set_keycode(code - Key::KEY_0 + Key::KP_0);
			}
		}
		if (_edit.mode == TRANSFORM_NONE) {
			if (_edit.gizmo.is_valid() && (k->get_keycode() == Key::ESCAPE || k->get_keycode() == Key::BACKSPACE)) {
				
				_edit.gizmo->commit_handle(_edit.gizmo_handle, _edit.gizmo_handle_secondary, _edit.gizmo_initial_value, true);
				_edit.gizmo = Ref<EditorNode3DGizmo>();
			}
			if (k->get_keycode() == Key::ESCAPE && !cursor.region_select) {
				_clear_selected();
				return;
			}
		} else {