Para 15.6 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:computersalat:certbot/15.6/home:computersalat:certbot.repo
zypper refresh
zypper install python-zope.event
Para 15.5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:computersalat:certbot/15.5/home:computersalat:certbot.repo
zypper refresh
zypper install python-zope.event
Para 15.4 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:computersalat:certbot/15.4/home:computersalat:certbot.repo
zypper refresh
zypper install python-zope.event