/usr/share/doc/libmysql-ruby1.8/changelog.Debian.gz is in libmysql-ruby1.8 2.8.2+gem2deb-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmysql-ruby1.8/../ruby-mysql/changelog.Debian.gz