### 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)

switch (EDITOR_GET(p_property).operator int()) {
		case 0:
			return Key::NONE;
		case 1:
			return Key::SHIFT;
		case 2:
			return Key::ALT;
		case 3:
			return Key::META;
		case 4:
			return Key::CTRL;
	}
	return Key::NONE;
}
static Key _get_key_modifier(Ref<InputEventWithModifiers> e) {
	if (e->is_shift_pressed()) {
		return Key::SHIFT;
	}
	if (e->is_alt_pressed()) {
		return Key::ALT;
	}
	if (e->is_ctrl_pressed()) {
		return Key::CTRL;
	}
	if (e->is_meta_pressed()) {
		return Key::META;
	}
	return Key::NONE;
}
bool Node3DEditorViewport::_transform_gizmo_select(const Vector2 &p_screenpos, bool p_highlight_only) {