Let ThreadPool exit gracefully. (#3653)

### What problem does this PR solve?

#3646

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/svr/task_executor.py

@@ -492,6 +492,7 @@ def report_status():
             logging.exception("report_status got exception")
         time.sleep(30)
 
+
 def analyze_heap(snapshot1: tracemalloc.Snapshot, snapshot2: tracemalloc.Snapshot, snapshot_id: int, dump_full: bool):
     msg = ""
     if dump_full:
@@ -508,6 +509,7 @@ def analyze_heap(snapshot1: tracemalloc.Snapshot, snapshot2: tracemalloc.Snapsho
         msg += '\n'.join(stat.traceback.format())
     logging.info(msg)
 
+
 def main():
     settings.init_settings()
     background_thread = threading.Thread(target=report_status)