$ git clone -n https://src.fedoraproject.org/rpms/R-packrat.git /var/lib/mock/f45-build-6292-347/root/chroot_tmpdir/scmroot/R-packrat
Cloning into '/var/lib/mock/f45-build-6292-347/root/chroot_tmpdir/scmroot/R-packrat'...
$ git fetch origin e2c468d08a3c955d6819541ae615d1b19bd0817b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-packrat
 * [new ref]         e2c468d08a3c955d6819541ae615d1b19bd0817b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e2c468d Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild