$ git clone -n https://src.fedoraproject.org/rpms/gthumb.git /var/lib/mock/f42-build-868892-176319/root/chroot_tmpdir/scmroot/gthumb
Cloning into '/var/lib/mock/f42-build-868892-176319/root/chroot_tmpdir/scmroot/gthumb'...
$ git fetch origin 655379a33605d73a62429f7bdf31e0ffd5c371b9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gthumb
 * [new ref]         655379a33605d73a62429f7bdf31e0ffd5c371b9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 655379a Rebuild for jpegxl (libjxl) 0.11.1