/etc/xdg/virt-builder/repos.d/opensuse.conf is in libguestfs-tools 1:1.36.13-1ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [opensuse.org]
uri=http://download.opensuse.org/repositories/Virtualization:/virt-builder-images/images/index
gpgkey=file:///etc/xdg/virt-builder/repos.d/opensuse.gpg
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