fix(event-handler): revert validator signature to Optional in oauth2.py

Revert client_secret_only_on_dev validator signature from str | None back to Optional[str] to fix FA102 ruff lint error.

PEP 604 union syntax in function signatures requires  `from __future__ import annotations` which conflicts with the existing FA100 noqa suppression in this file.

Part of #8088

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

Author: hirenkumar-n-dholariya

aws_lambda_powertools/event_handler/openapi/swagger_ui/oauth2.py

@@ -2,7 +2,7 @@
 from __future__ import annotations
 
 import warnings
-from typing import Sequence
+from typing import Optional, Sequence
 
 from pydantic import BaseModel, Field, field_validator
 
@@ -49,7 +49,7 @@ class OAuth2Config(BaseModel):
     model_config = MODEL_CONFIG_ALLOW
 
     @field_validator("clientSecret")
-    def client_secret_only_on_dev(cls, v: str | None) -> str | None:
+    def client_secret_only_on_dev(cls, v: Optional[str]) -> Optional[str]:
         if not v:
             return None