@Override
        public void run() {
            if (res.tryWrite(notModifiedHeaders)) {
                res.close();
            }
        }
Extends the request timeout by the specified {@code longPollingTimeoutMillis}, because otherwise
the client will get {@code "503 Service Unavailable} due to a {@link RequestTimeoutException} before
long-polling finishes.
core/src/main/java/com/linecorp/armeria/server/healthcheck/HealthCheckService.java