$ git clone -n https://src.fedoraproject.org/rpms/gstreamer1-plugins-base.git /var/lib/mock/f42-build-side-1-3523423-46206/root/chroot_tmpdir/scmroot/gstreamer1-plugins-base
Cloning into '/var/lib/mock/f42-build-side-1-3523423-46206/root/chroot_tmpdir/scmroot/gstreamer1-plugins-base'...
$ git fetch origin ade550a9547a3169693a6cf15e88921704e7e3c7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gstreamer1-plugins-base
 * [new ref]         ade550a9547a3169693a6cf15e88921704e7e3c7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ade550a BR libatomic