$ git clone -n https://src.fedoraproject.org/rpms/R-mockr.git /var/lib/mock/f40-build-1944524-25177/root/chroot_tmpdir/scmroot/R-mockr
Cloning into '/var/lib/mock/f40-build-1944524-25177/root/chroot_tmpdir/scmroot/R-mockr'...
$ git fetch origin c451970c3d223c3cd9ff2524811a6a70734ebeab:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-mockr
 * [new ref]         c451970c3d223c3cd9ff2524811a6a70734ebeab -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c451970 R-maint-sig mass rebuild