$ git clone -n https://src.fedoraproject.org/rpms/R-assertthat.git /var/lib/mock/f45-build-5972-345/root/chroot_tmpdir/scmroot/R-assertthat
Cloning into '/var/lib/mock/f45-build-5972-345/root/chroot_tmpdir/scmroot/R-assertthat'...
$ git fetch origin 62b04a9afc73954af8956df479b63b5792754d30:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-assertthat
 * [new ref]         62b04a9afc73954af8956df479b63b5792754d30 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 62b04a9 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild