[Bug] PopBufferMergeService 消息订阅者关系被移除

[MarvinYu]

Before Creating the Bug Report

• [x] I found a bug, not just asking a question, which should be created in GitHub Discussions.

• [x] I have searched the GitHub Issues and GitHub Discussions of this repository and believe that this is not a duplicate.

• [x] I have confirmed that this bug belongs to the current repository, not other repositories of RocketMQ.

Runtime platform environment

Linux or other

RocketMQ version

= 5.0.0

JDK Version

No response

Describe the Bug

PopBufferMergeService#scanGarbage 代码

if (System.currentTimeMillis() - entry.getValue().getTime() > minute5) {
    POP_LOGGER.info("[PopBuffer]remove long time not used sub {} of topic {} in buffer!", cid, topic);
    iterator.remove();
    continue;
}

对于一些开发和测试环境而言，因为消息比较少，topic与消费者订阅关系很容易被移除，然后出现消费者消息出现skip的情况。

Steps to Reproduce

消息发送者一天发送了5条消息，但是最终消费者只消费到其中三条

What Did You Expect to See?

消费者消息不丢失

What Did You See Instead?

消费者消息不丢失

Additional Context

No response