1. Use the fully qualified topic name on both the publisher and the subscriber (i.e. /gazebo/default/global_wind)
2. Did you try printing this instead of &wind_push::publ to see if that's also the same?
3. Why do you want to call gazebo::transport::fini() on your load function? That will finish the whole transport system, so no more pub/sub for anyone.
4. While running the simulation, run gz topic -i /gazebo/default/global_wind to see how many subscribers and publishers are there