For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:duwe:arm/openSUSE_Tumbleweed/home:duwe:arm.repo
zypper refresh
zypper install git-gui
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:duwe:arm/16.0/home:duwe:arm.repo
zypper refresh
zypper install git-gui
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:duwe:arm/15.6/home:duwe:arm.repo
zypper refresh
zypper install git-gui