/usr/share/doc/libgtk-3-dev/AUTHORS is in libgtk-3-dev 3.4.2-0ubuntu0.9.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtk-3-dev/../libgtk-3-0/AUTHORS
/usr/share/doc/libgtk-3-dev/../libgtk-3-0/AUTHORS