Graceful exit has not taken effect

**Version:**
system: macOS 14.4.1
node: 20.12.2
"egg": "^3.17.5",
"egg-cluster": "^2.2.1",

Minimal Code Example:

`npx egg-init --type simple`

```js
// router.js
module.exports = app => {
const { router, controller } = app;
router.get('/', controller.home.index);

// add a router has a 3 seconds aysnc job
router.get("/test", async (ctx) => {
await new Promise((resolve) => {
setTimeout(() => {
resolve(1);
}, 3000);
});
ctx.body = "test";
})

};

```

```js
// index.js
const startCluster = require('egg-cluster').startCluster;

startCluster({
baseDir: __dirname,
workers: 2,
port: 7001,
});
```

1. start command: node index.js
2. find node index.js `pid` in htop
3. curl -v http://127.0.0.1:7001/api/v1/test
4. send SIGTERM signal to pid filter in step 2

Expected: The request in step 3 has a successful response, EGG server closes after handling in transit connection.

Actually: the connection is closed immediately after the SIGTERM signal send.