/usr/share/doc/libmono-2.0-dev/changelog.Debian.gz is in libmono-2.0-dev 4.2.1.102+dfsg2-7ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmono-2.0-dev/../libmonoboehm-2.0-dev/changelog.Debian.gz