$ git clone -n https://github.com/xcp-ng-rpms/libarchive /var/lib/mock/v8.3-incoming-10639-29193/root/chroot_tmpdir/scmroot/libarchive
Cloning into '/var/lib/mock/v8.3-incoming-10639-29193/root/chroot_tmpdir/scmroot/libarchive'...
$ git fetch origin 4a24fd8a42e1739f1fba23481392d05b6e239232:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/libarchive
 * [new ref]         4a24fd8a42e1739f1fba23481392d05b6e239232 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4a24fd8 Merge pull request #1 from xcp-ng-rpms/8.3-XS-1557