### 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 camera_3d_override;
}
void Viewport::set_camera_3d_override_transform(const Transform3D &p_transform) {
	if (camera_3d_override) {
		camera_3d_override.transform = p_transform;
		RenderingServer::get_singleton()->camera_set_transform(camera_3d_override.rid, p_transform);
	}
}
Transform3D Viewport::get_camera_3d_override_transform() const {
	if (camera_3d_override) {
		return camera_3d_override.transform;
	}
	return Transform3D();
}
Ref<World3D> Viewport::get_world_3d() const {
	return world_3d;
}
Ref<World3D> Viewport::find_world_3d() const {
	if (own_world_3d.is_valid()) {
		return own_world_3d;
	} else if (world_3d.is_valid()) {
		return world_3d;
	} else if (parent) {
		return parent->find_world_3d();
	} else {
		return Ref<World3D>();
	}
}
void Viewport::set_world_3d(const Ref<World3D> &p_world_3d) {