$ git clone -n https://src.fedoraproject.org/rpms/gstreamer1-plugins-base.git /var/lib/mock/f42-build-side-1-3498682-45963/root/chroot_tmpdir/scmroot/gstreamer1-plugins-base
Cloning into '/var/lib/mock/f42-build-side-1-3498682-45963/root/chroot_tmpdir/scmroot/gstreamer1-plugins-base'...
$ git fetch origin cc18199fe6a5d96bec2b3d9ee6ec2d1adf205e03:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gstreamer1-plugins-base
 * [new ref]         cc18199fe6a5d96bec2b3d9ee6ec2d1adf205e03 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cc18199 1.26.0