### 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 own_world_3d.is_valid();
}
void Viewport::_propagate_enter_world_3d(Node *p_node) {
	if (p_node != this) {
		if (!p_node->is_inside_tree()) { 
			return;
		}
		if (Object::cast_to<Node3D>(p_node) || Object::cast_to<WorldEnvironment>(p_node)) {
			p_node->notification(Node3D::NOTIFICATION_ENTER_WORLD);
		} else {
			Viewport *v = Object::cast_to<Viewport>(p_node);
			if (v) {
				if (v->world_3d.is_valid() || v->own_world_3d.is_valid()) {
					return;
				}
			}
		}
	}
	for (int i = 0; i < p_node->get_child_count(); i++) {
		_propagate_enter_world_3d(p_node->get_child(i));
	}
}
void Viewport::_propagate_exit_world_3d(Node *p_node) {