$ git clone -n https://src.fedoraproject.org/rpms/gstreamer1-plugin-libav.git /var/lib/mock/f42-build-side-1-3585591-46906/root/chroot_tmpdir/scmroot/gstreamer1-plugin-libav
Cloning into '/var/lib/mock/f42-build-side-1-3585591-46906/root/chroot_tmpdir/scmroot/gstreamer1-plugin-libav'...
$ git fetch origin 90cf90352dc4a9473c692b6044a09107ff1930f1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gstreamer1-plugin-libav
 * [new ref]         90cf90352dc4a9473c692b6044a09107ff1930f1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 90cf903 1.26.3