Remove std::move from return statement

[ellert]

.../test/drunk-server/DrunkServer.cpp:116:23: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]
  116 |       return std::move(conn);
      |              ~~~~~~~~~^~~~~~
.../test/drunk-server/DrunkServer.cpp:116:23: note: remove 'std::move' call