tests/driver_soft_uart: Makefile.ci: add small stm32 boards
tests/driver_soft_uart: Makefile.ci: add small stm32 boards

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