fix(account.invoice): add text/xml mime type

sometimes the xml files are in text/xml format and to read it property it was necessary to add the format

l10n_mx_facturae_validate_cfdi/invoice.py

                     cr, uid,
                     [('res_id', '=', invoice.id),
                      ('res_model', '=', 'account.invoice'),
-                     '|',
-                     ('file_type', '=', 'application/xml'),
-                     ('file_type', '=', 'text/plain')],
+                     ('file_type', 'in',
+                      ('text/xml', 'application/xml', 'text/plain')), ],
                     context=context)
                 # Process and stores the info of the attachments
                 count = 0