fix unbound variables: "code", "message"

source: #1606 (comment)

Author: geetu040

openml/_api/clients/http.py

@@ -238,6 +238,8 @@ def _validate_response(
             raise OpenMLServerError(f"URI too long! ({url})")
 
         retry_raise_e: Exception | None = None
+        code: int | None = None
+        message: str = ""
 
         try:
             code, message = self._parse_exception_response(response)