add ~riscv keyword
tatt report: USE tests started on Thu Mar 9 21:05:19 CST 2023 FEATURES=' test' USE='' succeeded for =kde-apps/kleopatra-22.12.3 USE='-handbook -pim' succeeded for =kde-apps/kleopatra-22.12.3 USE='handbook -pim' succeeded for =kde-apps/kleopatra-22.12.3 USE='-handbook pim' succeeded for =kde-apps/kleopatra-22.12.3 USE='handbook pim' succeeded for =kde-apps/kleopatra-22.12.3
riscv done all arches done