fdo#82136 fix download of submodule tarballs

Change-Id: I07775391cb905f0563d1d1b3cae6f02b12d10f90
(cherry picked from commit 922b03f0818baa65e4c036f58fe7f8c29776b81e)
Reviewed-on: https://gerrit.libreoffice.org/10738
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>