$ git clone -n https://src.fedoraproject.org/rpms/linbox.git /var/lib/mock/f39-build-1752135-41467/root/chroot_tmpdir/scmroot/linbox
Cloning into '/var/lib/mock/f39-build-1752135-41467/root/chroot_tmpdir/scmroot/linbox'...
$ git fetch origin 8b2f55a2ab3a17c9efd3ed2b4fdeb258655e1c34:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/linbox
 * [new ref]         8b2f55a2ab3a17c9efd3ed2b4fdeb258655e1c34 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 8b2f55a Fix OpenCL support