### 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)

if (dist < (gizmo_scale * GIZMO_PLANE_SIZE * 1.5)) {
						const real_t d = ray_pos.distance_to(r);
						if (d < col_d) {
							col_d = d;
							col_axis = i;
							is_plane_scale = true;
						}
					}
				}
			}
		}
		if (col_axis != -1) {
			if (p_highlight_only) {
				spatial_editor->select_gizmo_highlight_axis(col_axis + (is_plane_scale ? 12 : 9));
			} else {
				
				_edit.mode = TRANSFORM_SCALE;
				_compute_edit(p_screenpos);
				_edit.plane = TransformPlane(TRANSFORM_X_AXIS + col_axis + (is_plane_scale ? 3 : 0));
			}
			return true;
		}
	}
	if (p_highlight_only) {
		spatial_editor->select_gizmo_highlight_axis(-1);
	}
	return false;
}
void Node3DEditorViewport::_transform_gizmo_apply(Node3D *p_node, const Transform3D &p_transform, bool p_local) {