For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Yoshio_Sato:branches:openSUSE:infrastructure:wiki/openSUSE_Tumbleweed/home:Yoshio_Sato:branches:openSUSE:infrastructure:wiki.repo
zypper refresh
zypper install mediawiki_1_44-UserMerge
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Yoshio_Sato:branches:openSUSE:infrastructure:wiki/15.6/home:Yoshio_Sato:branches:openSUSE:infrastructure:wiki.repo
zypper refresh
zypper install mediawiki_1_44-UserMerge