www/nyxt: Add i386 to NOT_FOR_ARCHS
Build depend lang/sbcl is only available to amd64 and i386.
Exclude nyxt from i386 since it isn't supported upstream as I investigated.
Error log:
https://pkg-status.freebsd.org/beefy18/data/143i386-default/0f586647e560/logs/nyxt-3.12.0_2.log
(cherry picked from commit badbfa0b333d55d43e7789cfc549d46ed49a8a25)