/usr/share/gtk-doc/html/glib is in libglib2.0-doc 2.56.1-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/gtk-doc/html/../../doc/libglib2.0-doc/glib
/usr/share/gtk-doc/html/../../doc/libglib2.0-doc/glib