$ git clone -n https://src.fedoraproject.org/rpms/R-R6.git /var/lib/mock/f42-build-side-1-3500317-45970/root/chroot_tmpdir/scmroot/R-R6
Cloning into '/var/lib/mock/f42-build-side-1-3500317-45970/root/chroot_tmpdir/scmroot/R-R6'...
$ git fetch origin c0a4e2c7634e7f73a014f0497762798bd1bf1683:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-R6
 * [new ref]         c0a4e2c7634e7f73a014f0497762798bd1bf1683 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c0a4e2c R-maint-sig mass rebuild