/usr/lib/ghc-doc/hoogle/gstreamer.txt is in libghc-gstreamer-doc 0.12.1.2-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-gstreamer-doc/html/gstreamer.txt