Cast excluded from sii as boolean before grouping

The value may be None which should be grouped with false values

Closes #13734
(grafted from a03bfd30614754924f6122b53e17016853ec751c)

--HG--
branch : 7.0

modules/account_es_sii/account.py

@@ -484,7 +484,7 @@ class InvoiceSII(ModelSQL, ModelView):
                     'Repercutida' if invoice.type == 'out' else 'Soportada')),
             ('sii_key', tax.es_sii_tax_key or ''),
             ('operation_key', tax.es_sii_operation_key or ''),
-            ('excluded', tax.es_exclude_from_sii),
+            ('excluded', bool(tax.es_exclude_from_sii)),
             ('product_key', product_type),
             )