/usr/share/glib-2.0/schemas/20_debian-edu+gdm.gschema.override is in debian-edu-artwork 0.902-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | [org.gnome.login-screen]
# - Disable user list
disable-user-list=true
|