add ~riscv keyword
Looks good on riscv USE tests started on Wed Nov 2 15:25:52 -00 2022 FEATURES=' test' USE='' succeeded for =www-apps/baikal-0.9.1 USE='-mysql sqlite vhosts' succeeded for =www-apps/baikal-0.9.1
keyworded in https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=312f7ca0a5655de20144417f0868c6c2a02313d0