Add return value to validate_region_zone for local cloud (skypilot-org#1518)

Add return value to validate_region_zone

Author: ewzeng

sky/clouds/local.py

@@ -157,3 +157,4 @@ def validate_region_zone(self, region: Optional[str], zone: Optional[str]):
         if region is None or region != Local.LOCAL_REGION.name:
             raise ValueError(f'Region {region!r} does not match the Local'
                              ' cloud region {Local.LOCAL_REGION.name!r}.')
+        return region, zone