### 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)
return size_2d_override;
}
bool Viewport::_is_size_allocated() const {
	return size_allocated;
}
Rect2 Viewport::get_visible_rect() const {
	Rect2 r;
	if (size == Size2()) {
		r = Rect2(Point2(), DisplayServer::get_singleton()->window_get_size());
	} else {
		r = Rect2(Point2(), size);
	}
	if (size_2d_override != Size2i()) {
		r.size = size_2d_override;
	}
	return r;
}
void Viewport::_update_audio_listener_2d() {