### 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)

const bool focused = focused_axis == p_axis.axis;
	const bool positive = p_axis.axis < 3;
	const int direction = p_axis.axis % 3;
	const Color axis_color = axis_colors[direction];
	const double alpha = focused ? 1.0 : ((p_axis.z_axis + 1.0) / 2.0) * 0.5 + 0.5;
	const Color c = focused ? Color(0.9, 0.9, 0.9) : Color(axis_color, alpha);
	if (positive) {
		
		const Vector2i center = get_size() / 2.0;
		draw_line(center, p_axis.screen_point, c, 1.5 * EDSCALE);
		draw_circle(p_axis.screen_point, AXIS_CIRCLE_RADIUS, c);
		
		const String axis_name = direction == 0 ? "X" : (direction == 1 ? "Y" : "Z");
		draw_char(get_theme_font(SNAME("rotation_control"), EditorStringName(EditorFonts)), p_axis.screen_point + Vector2i(Math::round(-4.0 * EDSCALE), Math::round(5.0 * EDSCALE)), axis_name, get_theme_font_size(SNAME("rotation_control_size"), EditorStringName(EditorFonts)), Color(0.0, 0.0, 0.0, alpha));
	} else {
		
		draw_circle(p_axis.screen_point, AXIS_CIRCLE_RADIUS, c);
		draw_circle(p_axis.screen_point, AXIS_CIRCLE_RADIUS * 0.8, c.darkened(0.4));
	}
}
void ViewportRotationControl::_get_sorted_axis(Vector<Axis2D> &r_axis) {