For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:ruby:extensions/openSUSE_Tumbleweed/devel:languages:ruby:extensions.repo
zypper refresh
zypper install rubygem-addressable
For assist repo checker run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:ruby:extensions/assist_repo_checker/devel:languages:ruby:extensions.repo
zypper refresh
zypper install rubygem-addressable
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:ruby:extensions/15.6/devel:languages:ruby:extensions.repo
zypper refresh
zypper install rubygem-addressable