/usr/share/doc/libgtkmm-2.4-dev/changelog.Debian.gz is in libgtkmm-2.4-dev 1:2.24.5-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtkmm-2.4-dev/../libgtkmm-2.4-1v5/changelog.Debian.gz