$ git clone -n https://src.fedoraproject.org/rpms/libb64.git /var/lib/mock/f45-build-15881-480/root/chroot_tmpdir/scmroot/libb64
Cloning into '/var/lib/mock/f45-build-15881-480/root/chroot_tmpdir/scmroot/libb64'...
$ git fetch origin bb74e119f9db65c13de9bdcc09bdad72a0e50367:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/libb64
 * [new ref]         bb74e119f9db65c13de9bdcc09bdad72a0e50367 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at bb74e11 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild