fix(core): ensure_ascii=False in PydanticOutputParser exception formatting (#34006)

- **Description:** When formatting an error, `PydanticOutputParser`
dumps json with default `ensure_ascii=True`
  -  **Issue:** Fixes #34005
  - **Dependencies:** None

- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. **We will not consider
a PR unless these three are passing in CI.** See [contribution
guidelines](https://docs.langchain.com/oss/python/contributing) for
more.

Co-authored-by: Mason Daugherty <mason@langchain.dev>

libs/core/langchain_core/output_parsers/pydantic.py

@@ -37,7 +37,7 @@ class PydanticOutputParser(JsonOutputParser, Generic[TBaseModel]):
     def _parser_exception(
         self, e: Exception, json_object: dict
     ) -> OutputParserException:
-        json_string = json.dumps(json_object)
+        json_string = json.dumps(json_object, ensure_ascii=False)
         name = self.pydantic_object.__name__
         msg = f"Failed to parse {name} from completion {json_string}. Got: {e}"
         return OutputParserException(msg, llm_output=json_string)