fix: correct indentation in dataset retrieval model assignment

Fix a bug that caused errors when uploading knowledge through the API by correcting the indentation level of the retrieval model assignment in dataset_service.py. The incorrect indentation was causing the retrieval model to be assigned outside the proper scope, leading to API errors during knowledge upload.

api/services/dataset_service.py

@@ -960,11 +960,11 @@ class DocumentService:
                         "score_threshold_enabled": False,
                     }
 
-                dataset.retrieval_model = (
+                    dataset.retrieval_model = (
-                    knowledge_config.retrieval_model.model_dump()
+                        knowledge_config.retrieval_model.model_dump()
-                    if knowledge_config.retrieval_model
+                        if knowledge_config.retrieval_model
-                    else default_retrieval_model
+                        else default_retrieval_model
-                )  # type: ignore
+                    )  # type: ignore
 
         documents = []
         if knowledge_config.original_document_id: