tests: prefer `asio::io_context` over `asio::io_service`

Change-Id: I368fad49dbf350ce09641ca3198ba5679ee6a27e
diff --git a/tests/io-key-chain-fixture.hpp b/tests/io-key-chain-fixture.hpp
index c88a700..a13e262 100644
--- a/tests/io-key-chain-fixture.hpp
+++ b/tests/io-key-chain-fixture.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2022, Regents of the University of California
+ * Copyright (c) 2014-2023, Regents of the University of California
  *
  * NAC library is free software: you can redistribute it and/or modify it under the
  * terms of the GNU Lesser General Public License as published by the Free Software
@@ -23,7 +23,7 @@
 #include "tests/clock-fixture.hpp"
 #include "tests/key-chain-fixture.hpp"
 
-#include <boost/asio/io_service.hpp>
+#include <boost/asio/io_context.hpp>
 
 namespace ndn::nac::tests {
 
@@ -34,17 +34,13 @@
   afterTick() final
   {
     if (m_io.stopped()) {
-#if BOOST_VERSION >= 106600
       m_io.restart();
-#else
-      m_io.reset();
-#endif
     }
     m_io.poll();
   }
 
 protected:
-  boost::asio::io_service m_io;
+  boost::asio::io_context m_io;
 };
 
 } // namespace ndn::nac::tests