/usr/lib/go-1.9/favicon.ico.gz is in golang-1.9-doc 1.9.4-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/go-1.9/../../share/doc/golang-1.9-doc/favicon.ico.gz
/usr/lib/go-1.9/../../share/doc/golang-1.9-doc/favicon.ico.gz