$ git clone -n https://src.fedoraproject.org/rpms/libgit2_1.6.git /var/lib/mock/f40-build-786066-134156/root/chroot_tmpdir/scmroot/libgit2_1.6
Cloning into '/var/lib/mock/f40-build-786066-134156/root/chroot_tmpdir/scmroot/libgit2_1.6'...
$ git fetch origin a220dd6655d52c70d283f031190f82537b3d0613:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/libgit2_1.6
 * [new ref]         a220dd6655d52c70d283f031190f82537b3d0613 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a220dd6 Update to 1.6.5