/usr/share/doc/libgsm0710-dbg/changelog.Debian.gz is in libgsm0710-dbg 1.2.1+git20100218-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgsm0710-dbg/../libgsm0710-0/changelog.Debian.gz