$ git clone -n https://src.fedoraproject.org/rpms/R-readr.git /var/lib/mock/f42-build-side-1-3501737-45976/root/chroot_tmpdir/scmroot/R-readr
Cloning into '/var/lib/mock/f42-build-side-1-3501737-45976/root/chroot_tmpdir/scmroot/R-readr'...
$ git fetch origin 11bbe276d844f0dad72f76f0428cf413adca5d2f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-readr
 * [new ref]         11bbe276d844f0dad72f76f0428cf413adca5d2f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 11bbe27 R-maint-sig mass rebuild