/usr/share/doc/libgtkmm-3.0-dev/changelog.Debian.gz is in libgtkmm-3.0-dev 3.22.2-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtkmm-3.0-dev/../libgtkmm-3.0-1v5/changelog.Debian.gz