### 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 (selection_in_progress && movement_threshold_passed) {
					if (get_selected_count() == 0 || clicked_wants_append) {
						cursor.region_select = true;
						cursor.region_begin = _edit.original_mouse_pos;
						clicked = ObjectID();
					}
				}
				if (cursor.region_select) {
					cursor.region_end = m->get_position();
					surface->queue_redraw();
					return;
				}
				if (clicked.is_valid() && movement_threshold_passed) {
					_compute_edit(_edit.original_mouse_pos);
					clicked = ObjectID();
					_edit.mode = TRANSFORM_TRANSLATE;
				}
				if (_edit.mode == TRANSFORM_NONE || _edit.numeric_input != 0 || _edit.numeric_next_decimal != 0) {
					return;
				}
				update_transform(_get_key_modifier(m) == Key::SHIFT);
			}
		} else if (m->get_button_mask().has_flag(MouseButtonMask::RIGHT) || freelook_active) {
			if (nav_scheme == NAVIGATION_MAYA && m->is_alt_pressed()) {
				nav_mode = NAVIGATION_ZOOM;
			} else if (freelook_active) {
				nav_mode = NAVIGATION_LOOK;
			} else if (orthogonal) {
				nav_mode = NAVIGATION_PAN;