### 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 int precision = freelook_speed < 1.0 ? 2 : 1;
					draw_indicator_bar(
							*surface,
							1.0 - logscale_t,
							get_editor_theme_icon(SNAME("ViewportSpeed")),
							get_theme_font(SNAME("font"), SNAME("Label")),
							get_theme_font_size(SNAME("font_size"), SNAME("Label")),
							vformat("%s m/s", String::num(freelook_speed).pad_decimals(precision)),
							Color(1.0, 0.95, 0.7));
				}
			} else {
				/
				zoom_limit_label->set_visible(zoom_failed_attempts_count > 15);
				real_t min_distance = MAX(camera->get_near() * 4, ZOOM_FREELOOK_MIN);
				real_t max_distance = MIN(camera->get_far() / 4, ZOOM_FREELOOK_MAX);
				real_t scale_length = (max_distance - min_distance);
				if (!Math::is_zero_approx(scale_length)) {
					real_t logscale_t = 1.0 - Math::log1p(cursor.distance - min_distance) / Math::log1p(scale_length);
					/
					const int precision = cursor.distance < 1.0 ? 2 : 1;
					draw_indicator_bar(
							*surface,
							logscale_t,
							get_editor_theme_icon(SNAME("ViewportZoom")),
							get_theme_font(SNAME("font"), SNAME("Label")),
							get_theme_font_size(SNAME("font_size"), SNAME("Label")),
							vformat("%s m", String::num(cursor.distance).pad_decimals(precision)),
							Color(0.7, 0.95, 1.0));
				}
			}