[fix] Session Data Not Persisting in POST Requests in Koa Application
## Describe the bug

**Node.js version:** <!-- Write your Node.js version. -->
v20.2.0
**OS version:** <!-- Write your operating system and version. -->
win11
**Description:** <!-- A clear and concise description of what the bug is. -->
I am encountering an issue in my Koa application where setting `ctx.session` works as expected in a GET request handler but does not work in a POST request handler. I expected the same behavior for both GET and POST requests.

## Actual behavior <!-- Write actual behavior here. -->
In the POST request handler, when I attempt to set `ctx.session.token = "guest-2"`, the session data does not get updated, and subsequent requests do not reflect the change. However, the same code works as expected in a GET request handler.
## Expected behavior
I expect to be able to set `ctx.session.token` in both GET and POST request handlers, and the session data should be updated accordingly.

<!-- Write expected behavior here. -->

## Code to reproduce
```js
 ...get(..., async (ctx) => {
      ctx.session.token = "guest"; //work
    });
 ...post(..., async (ctx) => {
      ctx.session.token = "guest-2";//not work
});
```
<!-- Share code to reproduce here inside a code formatted block, gist, or a repository we can clone to reproduce. -->

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## Checklist

- [ ✅] I have searched through GitHub issues for similar issues.
- [ ✅ ] I have completely read through the README and documentation.
- [ ✅ ] I have tested my code with the latest version of Node.js and this package and confirmed it is still not working.
