### 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)

int font_size = get_theme_font_size(SNAME("font_size"), SNAME("Label"));
		Point2 msgpos = Point2(5, get_size().y - 20);
		font->draw_string(ci, msgpos + Point2(1, 1), message, HORIZONTAL_ALIGNMENT_LEFT, -1, font_size, Color(0, 0, 0, 0.8));
		font->draw_string(ci, msgpos + Point2(-1, -1), message, HORIZONTAL_ALIGNMENT_LEFT, -1, font_size, Color(0, 0, 0, 0.8));
		font->draw_string(ci, msgpos, message, HORIZONTAL_ALIGNMENT_LEFT, -1, font_size, Color(1, 1, 1, 1));
	}
	if (_edit.mode == TRANSFORM_ROTATE && _edit.show_rotation_line) {
		Point2 center = _point_to_screen(_edit.center);
		Color handle_color;
		switch (_edit.plane) {
			case TRANSFORM_X_AXIS:
				handle_color = get_theme_color(SNAME("axis_x_color"), EditorStringName(Editor));
				break;
			case TRANSFORM_Y_AXIS:
				handle_color = get_theme_color(SNAME("axis_y_color"), EditorStringName(Editor));
				break;
			case TRANSFORM_Z_AXIS:
				handle_color = get_theme_color(SNAME("axis_z_color"), EditorStringName(Editor));
				break;
			default:
				handle_color = get_theme_color(SNAME("accent_color"), EditorStringName(Editor));
				break;
		}
		handle_color = handle_color.from_hsv(handle_color.get_h(), 0.25, 1.0, 1);
		RenderingServer::get_singleton()->canvas_item_add_line(
				ci,
				_edit.mouse_pos,
				center,
				handle_color,
				Math::round(2 * EDSCALE));