/usr/share/doc/libgnuradio-runtime3.7.9/changelog.Debian.gz is in libgnuradio-runtime3.7.9 3.7.9.1-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgnuradio-runtime3.7.9/../libgnuradio-pmt3.7.9/changelog.Debian.gz