/usr/share/doc/libmosquitto1-dbg/changelog.Debian.gz is in libmosquitto1-dbg 1.4.8-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmosquitto1-dbg/../libmosquitto1/changelog.Debian.gz