$ git clone -n https://github.com/xcp-ng-rpms/libarchive /var/lib/mock/v8.3-incoming-9071-27920/root/chroot_tmpdir/scmroot/libarchive
Cloning into '/var/lib/mock/v8.3-incoming-9071-27920/root/chroot_tmpdir/scmroot/libarchive'...
$ git fetch origin 15b03182a08bfd31c50e351fba6b0d794d510b04:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/libarchive
 * [new ref]         15b03182a08bfd31c50e351fba6b0d794d510b04 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 15b0318 Merge branch 'XS-8.3' into 8.3-XS-1557