### 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)
Control *over = gui_find_control(pos);
			if (over) {
				gui.touch_focus[touch_index] = over->get_instance_id();
				bool stopped = false;
				if (over->can_process()) {
					touch_event = touch_event->xformed_by(Transform2D()); 
					pos = over->get_global_transform_with_canvas().affine_inverse().xform(pos);
					touch_event->set_position(pos);
					stopped = _gui_call_input(over, touch_event);
				}
				if (stopped) {
					set_input_as_handled();
				}
				return;
			}
		} else {
			bool stopped = false;
			ObjectID control_id = gui.touch_focus[touch_index];
			Control *over = control_id.is_valid() ? Object::cast_to<Control>(ObjectDB::get_instance(control_id)) : nullptr;
			if (over && over->can_process()) {
				touch_event = touch_event->xformed_by(Transform2D()); 
				pos = over->get_global_transform_with_canvas().affine_inverse().xform(pos);
				touch_event->set_position(pos);
				stopped = _gui_call_input(over, touch_event);
			}
			if (stopped) {
				set_input_as_handled();
			}
			gui.touch_focus.erase(touch_index);
			return;