Fix mypy errors in Optuna 4.0+

python_tests/wsgi_client.py

@@ -10,6 +10,8 @@ from optuna_dashboard._storage import trials_last_fetched_at
 
 
 if typing.TYPE_CHECKING:
+    from sys import _OptExcInfo
+
     from _typeshed.wsgi import WSGIEnvironment
 
 
@@ -64,7 +66,9 @@ def send_request(
     status: str = ""
     response_headers: list[tuple[str, str]] = []
 
-    def start_response(status_: str, headers_: list[tuple[str, str]]) -> None:
+    def start_response(
+        status_: str, headers_: list[tuple[str, str]], exc_info: _OptExcInfo | None = None
+    ) -> None:
         nonlocal status, response_headers
         status = status_
         response_headers = headers_