$ git clone -n https://github.com/xcp-ng-rpms/trousers /var/lib/mock/v8.3-incoming-10641-29195/root/chroot_tmpdir/scmroot/trousers
Cloning into '/var/lib/mock/v8.3-incoming-10641-29195/root/chroot_tmpdir/scmroot/trousers'...
$ git fetch origin dcd80e768a954e5fc9aa888f88dcda4e54af29e2:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/trousers
 * [new ref]         dcd80e768a954e5fc9aa888f88dcda4e54af29e2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at dcd80e7 Merge pull request #1 from xcp-ng-rpms/8.3-XS-1557