add ~riscv keyword
tatt report: USE tests started on Tue Feb 14 23:38:55 CST 2023 FEATURES=' test' USE='' succeeded for =media-gfx/simple-scan-42.5 USE='-colord -webp' succeeded for =media-gfx/simple-scan-42.5 USE='colord -webp' succeeded for =media-gfx/simple-scan-42.5 USE='-colord webp' succeeded for =media-gfx/simple-scan-42.5 USE='colord webp' succeeded for =media-gfx/simple-scan-42.5 an simple doc scan app for documentation have not manual test
riscv done all arches done