### 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 world_2d;
}
Camera2D *Viewport::get_camera_2d() const {
	return camera_2d;
}
Transform2D Viewport::get_final_transform() const {
	return _get_input_pre_xform().affine_inverse() * stretch_transform * global_canvas_transform;
}
void Viewport::assign_next_enabled_camera_2d(const StringName &p_camera_group) {
	List<Node *> camera_list;
	get_tree()->get_nodes_in_group(p_camera_group, &camera_list);
	Camera2D *new_camera = nullptr;
	for (const Node *E : camera_list) {
		const Camera2D *cam = Object::cast_to<Camera2D>(E);
		if (cam->is_enabled()) {
			new_camera = const_cast<Camera2D *>(cam);
			break;
		}
	}
	_camera_2d_set(new_camera);
	if (!camera_2d) {
		set_canvas_transform(Transform2D());
	}
}
void Viewport::_update_canvas_items(Node *p_node) {