[Chore/Refactor] Use centralized naive_utc_now for UTC datetime operations (#24352)

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/tasks/document_indexing_update_task.py

@@ -1,4 +1,3 @@
-import datetime
 import logging
 import time
 
@@ -8,6 +7,7 @@ from celery import shared_task  # type: ignore
 from core.indexing_runner import DocumentIsPausedError, IndexingRunner
 from core.rag.index_processor.index_processor_factory import IndexProcessorFactory
 from extensions.ext_database import db
+from libs.datetime_utils import naive_utc_now
 from models.dataset import Dataset, Document, DocumentSegment
 
 
@@ -31,7 +31,7 @@ def document_indexing_update_task(dataset_id: str, document_id: str):
         return
 
     document.indexing_status = "parsing"
-    document.processing_started_at = datetime.datetime.now(datetime.UTC).replace(tzinfo=None)
+    document.processing_started_at = naive_utc_now()
     db.session.commit()
 
     # delete all document segment and index