/usr/share/gtk-doc/html/libgnome is in libgnome2-doc 2.32.1-5ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/gtk-doc/html/../../doc/libgnome2-doc/html
/usr/share/gtk-doc/html/../../doc/libgnome2-doc/html