### Godot version

v4.0.beta.custom_build [0a9e6e478]

### System information

Ubuntu, Nvidia, Vulkan

### Issue description

When a Camera2D is freed - either explicitly or by being a child of a scene that is being switched away from via a method like `get_tree().change_scene_to_file()` - then this camera somehow stays active instead of Godot properly switching to no-camera-mode.

`get_viewport().get_camera_2d()` then returns all sorts of funny things from `<Freed Object>`  (it's supposed to return `null`) to arbitrary nodes of the current scene (not cameras).

This can lead to crashes.

### Steps to reproduce

checkout the MRP.

note that the "Go to scene 2" button switches places after pressing it.
that is because a camera is still active that does not exist in the current tree.

restart it a couple of times and spam the "Go to scene 2" button.
notice the garbage output.

### Minimal reproduction project

[godot_4_camera_bug.zip](https://github.com/godotengine/godot/files/10560455/godot_4_camera_bug.zip)
#include "viewport.h"
#include "core/config/project_settings.h"
#include "core/core_string_names.h"
#include "core/debugger/engine_debugger.h"
#include "core/object/message_queue.h"
#include "core/string/translation.h"
#include "core/templates/pair.h"
#include "scene/2d/audio_listener_2d.h"
#include "scene/2d/camera_2d.h"
#include "scene/2d/collision_object_2d.h"
#ifndef _3D_DISABLED
#include "scene/3d/audio_listener_3d.h"
#include "scene/3d/camera_3d.h"
#include "scene/3d/collision_object_3d.h"
#include "scene/3d/world_environment.h"
#endif 
#include "scene/gui/control.h"
#include "scene/gui/label.h"
#include "scene/gui/popup.h"
#include "scene/gui/popup_menu.h"
#include "scene/gui/subviewport_container.h"
#include "scene/main/canvas_layer.h"
#include "scene/main/window.h"