add ~riscv keyword
tatt build report: USE tests started on Wed Nov 2 13:45:42 CST 2022 FEATURES=' test' USE='' succeeded for =net-misc/x11-ssh-askpass-1.2.4.1-r2 USE='' succeeded for =net-misc/x11-ssh-askpass-1.2.4.1-r2
riscv done all arches done