Fix: Ensure lock is released in update_progress using context manager (#6975)

ragflow: v0.17 also encountered this problem. #1453 The task table shows
that the actual task has been completed. Since the process_msg of the
task is not synchronized to the document table, there is no progress
update on the page.
This may be caused by the lock not being released when the exception
occurs.

ragflow：v0.17同样碰到这个问题， 看task表实际任务已经完成，由于没有把task的process_msg同步给document表,
所以在页面看没有进度更新。
可能是这里异常时没有释放锁导致的。

```/api/ragflow_server.py
def update_progress():
    lock_value = str(uuid.uuid4())
    redis_lock = RedisDistributedLock("update_progress", lock_value=lock_value, timeout=60)
    logging.info(f"update_progress lock_value: {lock_value}")
    while not stop_event.is_set():
        try:
            if redis_lock.acquire():
                DocumentService.update_progress()
                redis_lock.release()
            stop_event.wait(6)
        except Exception:
            logging.exception("update_progress exception")
++       if redis_lock.acquired:
++               redis_lock.release()
```

api/ragflow_server.py

@@ -61,6 +61,8 @@ def update_progress():
             stop_event.wait(6)
         except Exception:
             logging.exception("update_progress exception")
+            if redis_lock.acquired:
+                redis_lock.release()
 
 def signal_handler(sig, frame):
     logging.info("Received interrupt signal, shutting down...")