Woops, fix missing `api_url` ref in error log

piker/brokers/kucoin.py

@@ -308,6 +308,7 @@ class Client:
         if data := json.get('data'):
             return data
         else:
+            api_url: str = self._http.base_url
             log.error(
                 f'Error making request to {api_url} ->\n'
                 f'{pformat(res)}'