$ git clone -n https://github.com/xcp-ng-rpms/libtasn1 /var/lib/mock/v8.3-incoming-10900-29394/root/chroot_tmpdir/scmroot/libtasn1
Cloning into '/var/lib/mock/v8.3-incoming-10900-29394/root/chroot_tmpdir/scmroot/libtasn1'...
$ git fetch origin 9ebf59afc3fa8b1499557d6902afa504bd8860e6:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/libtasn1
 * [new ref]         9ebf59afc3fa8b1499557d6902afa504bd8860e6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9ebf59a Import libtasn1-4.21.0-1.xs8.src.rpm