### 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)
Transform2D sxform = stretch_transform * global_canvas_transform;
	RenderingServer::get_singleton()->viewport_set_global_canvas_transform(viewport, sxform);
}
void Viewport::set_global_canvas_transform(const Transform2D &p_transform) {
	global_canvas_transform = p_transform;
	_update_global_transform();
}
Transform2D Viewport::get_global_canvas_transform() const {
	return global_canvas_transform;
}
void Viewport::_camera_2d_set(Camera2D *p_camera_2d) {
	camera_2d = p_camera_2d;
}
void Viewport::_audio_listener_2d_set(AudioListener2D *p_listener) {
	if (audio_listener_2d == p_listener) {
		return;
	} else if (audio_listener_2d) {
		audio_listener_2d->clear_current();
	}
	audio_listener_2d = p_listener;
}
void Viewport::_audio_listener_2d_remove(AudioListener2D *p_listener) {
	if (audio_listener_2d == p_listener) {
		audio_listener_2d = nullptr;
	}
}
void Viewport::_canvas_layer_add(CanvasLayer *p_canvas_layer) {
	canvas_layers.insert(p_canvas_layer);
}
void Viewport::_canvas_layer_remove(CanvasLayer *p_canvas_layer) {