### 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)

}
			bool current_hover_handle_secondary = false;
			int curreny_hover_handle = spatial_editor->get_current_hover_gizmo_handle(current_hover_handle_secondary);
			if (found_gizmo != spatial_editor->get_current_hover_gizmo() || found_handle != curreny_hover_handle || found_handle_secondary != current_hover_handle_secondary) {
				spatial_editor->set_current_hover_gizmo(found_gizmo);
				spatial_editor->set_current_hover_gizmo_handle(found_handle, found_handle_secondary);
				spatial_editor->get_single_selected_node()->update_gizmos();
			}
		}
		if (spatial_editor->get_current_hover_gizmo().is_null() && !m->get_button_mask().has_flag(MouseButtonMask::LEFT) && !_edit.gizmo.is_valid()) {
			_transform_gizmo_select(_edit.mouse_pos, true);
		}
		NavigationScheme nav_scheme = (NavigationScheme)EDITOR_GET("editors/3d/navigation/navigation_scheme").operator int();
		NavigationMode nav_mode = NAVIGATION_NONE;
		if (_edit.gizmo.is_valid()) {
			_edit.gizmo->set_handle(_edit.gizmo_handle, _edit.gizmo_handle_secondary, camera, m->get_position());
			Variant v = _edit.gizmo->get_handle_value(_edit.gizmo_handle, _edit.gizmo_handle_secondary);
			String n = _edit.gizmo->get_handle_name(_edit.gizmo_handle, _edit.gizmo_handle_secondary);
			set_message(n + ": " + String(v));
		} else if (m->get_button_mask().has_flag(MouseButtonMask::LEFT)) {
			if (nav_scheme == NAVIGATION_MAYA && m->is_alt_pressed()) {
				nav_mode = NAVIGATION_ORBIT;
			} else if (nav_scheme == NAVIGATION_MODO && m->is_alt_pressed() && m->is_shift_pressed()) {
				nav_mode = NAVIGATION_PAN;
			} else if (nav_scheme == NAVIGATION_MODO && m->is_alt_pressed() && m->is_command_or_control_pressed()) {
				nav_mode = NAVIGATION_ZOOM;
			} else if (nav_scheme == NAVIGATION_MODO && m->is_alt_pressed()) {
				nav_mode = NAVIGATION_ORBIT;
			} else {
				const bool movement_threshold_passed = _edit.original_mouse_pos.distance_to(_edit.mouse_pos) > 8 * EDSCALE;