rubygem-ffi from home:fsirl:ruby project

For 15.7 run the following as root:

zypper addrepo https://download.opensuse.org/repositories/home:fsirl:ruby/15.7/home:fsirl:ruby.repo
zypper refresh
zypper install rubygem-ffi

For 15.6 run the following as root:

zypper addrepo https://download.opensuse.org/repositories/home:fsirl:ruby/15.6/home:fsirl:ruby.repo
zypper refresh
zypper install rubygem-ffi