### 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)

tr.basis = t.basis * tr.basis;
			tr.origin += t.origin;
		}
		undo_redo->add_do_method(sp, "set_global_transform", tr);
		undo_redo->add_undo_method(sp, "set_global_transform", sp->get_global_gizmo_transform());
	}
	undo_redo->commit_action();
}
void Node3DEditor::_menu_item_toggled(bool pressed, int p_option) {
	switch (p_option) {
		case MENU_TOOL_LOCAL_COORDS: {
			tool_option_button[TOOL_OPT_LOCAL_COORDS]->set_pressed(pressed);
			update_transform_gizmo();
		} break;
		case MENU_TOOL_USE_SNAP: {
			tool_option_button[TOOL_OPT_USE_SNAP]->set_pressed(pressed);
			snap_enabled = pressed;
		} break;
		case MENU_TOOL_OVERRIDE_CAMERA: {
			EditorDebuggerNode *const debugger = EditorDebuggerNode::get_singleton();
			using Override = EditorDebuggerNode::CameraOverride;
			if (pressed) {
				debugger->set_camera_override((Override)(Override::OVERRIDE_3D_1 + camera_override_viewport_id));
			} else {
				debugger->set_camera_override(Override::OVERRIDE_NONE);
			}
		} break;
	}
}
void Node3DEditor::_menu_gizmo_toggled(int p_option) {