fix PEPPOL-EN16931-R053 in CII

the rule implies a cardinality change of BT-110 "Invoice total VAT amount" from 0..1 to 1..1 and needs to be changed to

<assert id="PEPPOL-EN16931-R053"
                 test="count(ram:SpecifiedTradeSettlementHeaderMonetarySummation/ram:TaxTotalAmount[@currencyID = $documentCurrencyCode]) &lt;= 1"
                 flag="warning">Maximum one tax total amount must be provided where currency id equals document currency code.</assert>