$ git clone -n https://src.fedoraproject.org/rpms/R-readr.git /var/lib/mock/f38-build-724257-99404/root/chroot_tmpdir/scmroot/R-readr
Cloning into '/var/lib/mock/f38-build-724257-99404/root/chroot_tmpdir/scmroot/R-readr'...
$ git fetch origin 0d3a78038e6f600a92a1c5b71f2e8f6a9c1ea8fd:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-readr
 * [new ref]         0d3a78038e6f600a92a1c5b71f2e8f6a9c1ea8fd -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0d3a780 Ignore vignettes