deal db session in celery worker (#17549)

api/tasks/annotation/add_annotation_to_index_task.py

@@ -6,6 +6,7 @@ from celery import shared_task  # type: ignore
 
 from core.rag.datasource.vdb.vector_factory import Vector
 from core.rag.models.document import Document
+from extensions.ext_database import db
 from models.dataset import Dataset
 from services.dataset_service import DatasetCollectionBindingService
 
@@ -55,3 +56,5 @@ def add_annotation_to_index_task(
         )
     except Exception:
         logging.exception("Build index for annotation failed")
+    finally:
+        db.session.close()