/usr/lib/x86_64-linux-gnu/libavahi-ui-gtk3.so is in libavahi-ui-gtk3-dev 0.6.30-5ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libavahi-ui-gtk3.so.0.1.4
/usr/lib/x86_64-linux-gnu/libavahi-ui-gtk3.so.0.1.4