$ git clone -n https://src.fedoraproject.org/rpms/R-cachem.git /var/lib/mock/f38-build-724991-99532/root/chroot_tmpdir/scmroot/R-cachem
Cloning into '/var/lib/mock/f38-build-724991-99532/root/chroot_tmpdir/scmroot/R-cachem'...
$ git fetch origin 2aef28b632bcde7b873ba1e85ac5d5d25d138944:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-cachem
 * [new ref]         2aef28b632bcde7b873ba1e85ac5d5d25d138944 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2aef28b Fix BuildRequires