erp5_accounting_l10n_fr: Make sure that FEC XML output is always the same given the same data.
I'm merging changes made for a customer project (@cedric.leninivin) into generic ERP5 and I remembered that @jerome had a comment (https://lab.nexedi.com/nexedi/erp5/commit/1a02ac9ceba4e88f9fe9f38ef4874ed7fac4af3c#note_66987) about this commit so here is a merge request for this particular change.