/usr/share/doc/exim4-daemon-heavy-dbg/changelog.Debian.gz is in exim4-daemon-heavy-dbg 4.76-3ubuntu3.4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/exim4-daemon-heavy-dbg/../exim4-base/changelog.Debian.gz