[sync.py] use add not append for sets (#9880)
[sync.py] use add not append for sets (#9880)

* [sync.py] use add not append for sets

Also add more logging

* fix
hail-is/hail,hail-is/hail,hail-is/hail,hail-is/hail,hail-is/hail,hail-is/hail,hail-is/hail,hail-is/hail