Since https://github.com/bornhack/bornhack-website/pull/1838, users can
set their preferred username there, so it can be correctly propagated
to Keycloak.
Change-Id: If492d4b92b420c07b9e1450883ccb30a18802a42
Reviewed-on: https://cl.snix.dev/c/snix/+/30424
Tested-by: besadii
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Autosubmit: Florian Klink <flokli@flokli.de>