Disallow pushing directly to git
Currently, we need to allow developers access to push directly to git so that the Damned Lies translation workflow continues to work. Once https://gitlab.gnome.org/GNOME/damned-lies/issues/78 is fixed, we can turn that off, and prevent anyone from pushing to the
glib-* branches. We can continue to allow people to push to
* branches so that they don’t need to fork the repository.