### 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)
ERR_FAIL_COND(world_3d.is_null());
	ERR_FAIL_COND(own_world_3d.is_null());
	if (is_inside_tree()) {
		_propagate_exit_world_3d(this);
	}
	own_world_3d = world_3d->duplicate();
	if (is_inside_tree()) {
		_propagate_enter_world_3d(this);
	}
	if (is_inside_tree()) {
		RenderingServer::get_singleton()->viewport_set_scenario(viewport, find_world_3d()->get_scenario());
	}
	_update_audio_listener_3d();
}
void Viewport::set_use_own_world_3d(bool p_use_own_world_3d) {