### 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)

sun_angle_azimuth->set_step(0.1);
		sun_angle_azimuth->set_allow_greater(true);
		sun_angle_azimuth->set_allow_lesser(true);
		sun_angle_azimuth->connect("value_changed", callable_mp(this, &Node3DEditor::_sun_direction_angle_set).unbind(1));
		sun_angle_azimuth_vbox->add_child(sun_angle_azimuth);
		sun_angle_hbox->add_child(sun_angle_azimuth_vbox);
		sun_angle_hbox->add_theme_constant_override("separation", 10);
		sun_vb->add_child(sun_angle_hbox);
		sun_color = memnew(ColorPickerButton);
		sun_color->set_edit_alpha(false);
		sun_vb->add_margin_child(TTR("Sun Color"), sun_color);
		sun_color->connect("color_changed", callable_mp(this, &Node3DEditor::_preview_settings_changed).unbind(1));
		sun_color->get_popup()->connect("about_to_popup", callable_mp(EditorNode::get_singleton(), &EditorNode::setup_color_picker).bind(sun_color->get_picker()));
		sun_energy = memnew(EditorSpinSlider);
		sun_energy->set_max(64.0);
		sun_energy->set_min(0);
		sun_energy->set_step(0.05);
		sun_vb->add_margin_child(TTR("Sun Energy"), sun_energy);
		sun_energy->connect("value_changed", callable_mp(this, &Node3DEditor::_preview_settings_changed).unbind(1));
		sun_max_distance = memnew(EditorSpinSlider);
		sun_vb->add_margin_child(TTR("Shadow Max Distance"), sun_max_distance);
		sun_max_distance->connect("value_changed", callable_mp(this, &Node3DEditor::_preview_settings_changed).unbind(1));
		sun_max_distance->set_min(1);
		sun_max_distance->set_max(4096);
		sun_add_to_scene = memnew(Button);
		sun_add_to_scene->set_text(TTR("Add Sun to Scene"));
		sun_add_to_scene->set_tooltip_text(TTR("Adds a DirectionalLight3D node matching the preview sun settings to the current scene.\nHold Shift while clicking to also add the preview environment to the current scene."));
		sun_add_to_scene->connect("pressed", callable_mp(this, &Node3DEditor::_add_sun_to_scene).bind(false));
		sun_vb->add_spacer();
		sun_vb->add_child(sun_add_to_scene);