add ~riscv keyword
The terminal used frequently tatt build report: USE tests started on Thu Feb 23 17:39:43 CST 2023 FEATURES=' test' USE='' succeeded for =kde-apps/yakuake-22.12.2 USE='-absolute-position' succeeded for =kde-apps/yakuake-22.12.2 USE='absolute-position' succeeded for =kde-apps/yakuake-22.12.2
riscv done all arches done