$ git clone -n https://src.fedoraproject.org/rpms/R-pbdRPC.git /var/lib/mock/f42-build-side-1-3501316-45974/root/chroot_tmpdir/scmroot/R-pbdRPC
Cloning into '/var/lib/mock/f42-build-side-1-3501316-45974/root/chroot_tmpdir/scmroot/R-pbdRPC'...
$ git fetch origin f8ee23c4dd2bf71d69ee3d02532a077643c89418:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-pbdRPC
 * [new ref]         f8ee23c4dd2bf71d69ee3d02532a077643c89418 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f8ee23c R-maint-sig mass rebuild