$ git clone -n https://github.com/xcp-ng-rpms/tcpdump.git /var/lib/mock/v8.3-incoming-10045-28689/root/chroot_tmpdir/scmroot/tcpdump
Cloning into '/var/lib/mock/v8.3-incoming-10045-28689/root/chroot_tmpdir/scmroot/tcpdump'...
$ git fetch origin 1cb75ee74db9ab08a94721efd3f416a02df92016:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/tcpdump
 * [new ref]         1cb75ee74db9ab08a94721efd3f416a02df92016 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1cb75ee Import tcpdump-4.9.2-3.el7.src.rpm