$ git clone -n https://github.com/xcp-ng-rpms/tcpdump.git /var/lib/mock/v8.3-incoming-10049-28689/root/chroot_tmpdir/scmroot/tcpdump
Cloning into '/var/lib/mock/v8.3-incoming-10049-28689/root/chroot_tmpdir/scmroot/tcpdump'...
$ git fetch origin e9d91ee46fafc24cecefd35cf120ba53bbdb4f10:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/tcpdump
 * [new ref]         e9d91ee46fafc24cecefd35cf120ba53bbdb4f10 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e9d91ee Add gcc to BuildRequires