pub async fn set_not_serving<S>(&self)
    where
        S: NamedService,
    {
        let service_name = <S as NamedService>::NAME;
        self.set_service_status(service_name, ServingStatus::NotServing)
            .await;
    }
Sets the status of the service implemented by `S` to `NotServing`. This notifies any watchers
if there is a change in status.
tonic-health/src/server.rs