[FIX] base_vat_autocomplete: add compatibility with python-stdnum>=1.9

The `country_codes` variable was replaced by `_country_codes` at
arthurdejong/python-stdnum@c113613b70

Make sure the syntax is the same

Closes #24395

addons/base_vat_autocomplete/models/res_partner.py

@@ -12,6 +12,9 @@ _logger = logging.getLogger(__name__)
 
 try:
     import stdnum.eu.vat as stdnum_vat
+    if not hasattr(stdnum_vat, "country_codes"):
+        # stdnum version >= 1.9
+        stdnum_vat.country_codes = stdnum_vat._country_codes
 except ImportError:
     _logger.warning('Python `stdnum` library not found, unable to call VIES service to detect address based on VAT number.')
     stdnum_vat = None