publish_send_op.cpp no longer compiles

[pdimov]

[ 86%] Building CXX object libs/mqtt5/test/CMakeFiles/boost_mqtt5-tests.dir/unit/publish_send_op.cpp.o
/home/runner/work/boost/boost/libs/mqtt5/test/unit/logger.cpp: In member function ‘boost::asio::ip::basic_resolver<boost::asio::ip::tcp>::results_type logger_tests::resolve_test_data::endpoints()’:
/home/runner/work/boost/boost/libs/mqtt5/test/unit/logger.cpp:106:25: error: ‘system_executor’ is not a member of ‘boost::asio’; did you mean ‘uses_executor’?
  106 |         auto ex = asio::system_executor {};
      |                         ^~~~~~~~~~~~~~~
      |                         uses_executor

Looks like the latest and greatest Asio changes have broken it.