gdm-branding-upstream from SUSE:SLE-15-SP4:Update project

需要 pool ，用 root 執行：

zypper addrepo https://download.opensuse.org/repositories/SUSE:SLE-15-SP4:Update/pool/SUSE:SLE-15-SP4:Update.repo
zypper refresh
zypper install gdm-branding-upstream