$ git clone -n https://src.fedoraproject.org/rpms/R-bit64.git /var/lib/mock/f45-build-5985-345/root/chroot_tmpdir/scmroot/R-bit64
Cloning into '/var/lib/mock/f45-build-5985-345/root/chroot_tmpdir/scmroot/R-bit64'...
$ git fetch origin b2cfa6e078ccd557a3515dedd01f64a7105a735e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-bit64
 * [new ref]         b2cfa6e078ccd557a3515dedd01f64a7105a735e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b2cfa6e Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild