$ git clone -n https://src.fedoraproject.org/rpms/R-callr.git /var/lib/mock/f45-build-5999-345/root/chroot_tmpdir/scmroot/R-callr
Cloning into '/var/lib/mock/f45-build-5999-345/root/chroot_tmpdir/scmroot/R-callr'...
$ git fetch origin 75c23f56aa9ff7a881c6b57308329c26027914c5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-callr
 * [new ref]         75c23f56aa9ff7a881c6b57308329c26027914c5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 75c23f5 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild