### 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)
physics_has_last_mousepos = false;
	_cleanup_mouseover_colliders(true, p_paused_only);
#ifndef _3D_DISABLED
	if (physics_object_over.is_valid()) {
		CollisionObject3D *co = Object::cast_to<CollisionObject3D>(ObjectDB::get_instance(physics_object_over));
		if (co) {
			if (!co->is_inside_tree()) {
				physics_object_over = ObjectID();
				physics_object_capture = ObjectID();
			} else if (!(p_paused_only && co->can_process())) {
				co->_mouse_exit();
				physics_object_over = ObjectID();
				physics_object_capture = ObjectID();
			}
		}
	}
#endif 
}
void Viewport::_cleanup_mouseover_colliders(bool p_clean_all_frames, bool p_paused_only, uint64_t p_frame_reference) {