$ git clone -n https://src.fedoraproject.org/rpms/cosmic-bg.git /var/lib/mock/f41-build-side-1-3108708-39383/root/chroot_tmpdir/scmroot/cosmic-bg
Cloning into '/var/lib/mock/f41-build-side-1-3108708-39383/root/chroot_tmpdir/scmroot/cosmic-bg'...
$ git fetch origin 9e0f87494c97c1efc03566ca80d5ea61b96bb3e2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/cosmic-bg
 * [new ref]         9e0f87494c97c1efc03566ca80d5ea61b96bb3e2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9e0f874 Use system backgrounds by default