Fix update_progress issue (#6992)

### What problem does this PR solve?

Fix update_progress issue introduced by #6975 

### Type of change

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

api/ragflow_server.py

             stop_event.wait(6)
         except Exception:
             logging.exception("update_progress exception")
-            if redis_lock.acquired:
-                redis_lock.release()
+        finally:
+            redis_lock.release()
 
 def signal_handler(sig, frame):
     logging.info("Received interrupt signal, shutting down...")