tests/Kconfig: add serpente to whitelist
tests/Kconfig: add serpente to whitelist

kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT,authmillenon/RIOT,authmillenon/RIOT,ant9000/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,miri64/RIOT,RIOT-OS/RIOT,miri64/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,miri64/RIOT,authmillenon/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,miri64/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kaspar030/RIOT,authmillenon/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,jasonatran/RIOT,ant9000/RIOT,miri64/RIOT,ant9000/RIOT,jasonatran/RIOT,kYc0o/RIOT,kaspar030/RIOT,authmillenon/RIOT,kYc0o/RIOT,kaspar030/RIOT