ai21[patch]: Update @root_validators for pydantic2 migration (#25401)

Update @root_validators for pydantic 2 migration.

libs/partners/ai21/langchain_ai21/ai21_base.py

@@ -28,7 +28,7 @@ class AI21Base(BaseModel):
     num_retries: Optional[int] = None
     """Maximum number of retries for API requests before giving up."""
 
-    @root_validator()
+    @root_validator(pre=True)
     def validate_environment(cls, values: Dict) -> Dict:
         api_key = convert_to_secret_str(
             values.get("api_key") or os.getenv("AI21_API_KEY") or ""
@@ -46,7 +46,13 @@ class AI21Base(BaseModel):
             os.getenv("AI21_TIMEOUT_SEC", _DEFAULT_TIMEOUT_SEC)
         )
         values["timeout_sec"] = timeout_sec
+        return values
 
+    @root_validator(pre=False, skip_on_failure=True)
+    def post_init(cls, values: Dict) -> Dict:
+        api_key = values["api_key"]
+        api_host = values["api_host"]
+        timeout_sec = values["timeout_sec"]
         if values.get("client") is None:
             values["client"] = AI21Client(
                 api_key=api_key.get_secret_value(),