$ git clone -n https://src.fedoraproject.org/rpms/rubygem-gstreamer.git /var/lib/mock/f39-build-1596719-38395/root/chroot_tmpdir/scmroot/rubygem-gstreamer
Cloning into '/var/lib/mock/f39-build-1596719-38395/root/chroot_tmpdir/scmroot/rubygem-gstreamer'...
$ git fetch origin e234f17b83cc500577979d8049a068b8607a6992:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-gstreamer
 * [new ref]         e234f17b83cc500577979d8049a068b8607a6992 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e234f17 4.2.0 entry