[fix] Request not being properly disposed when it encounters an error

## Describe the bug

**Node.js version:** 18.20.4

**OS version:** MacOs Sequoia 15.2

**Description:** After causing the request to crash by supplying undefined headers, the request is not properly closed and this causes a dangling handle that lasts for a few seconds.

## Actual behavior

## Expected behavior

The request should be ended, even if there are unexpected exceptions.

## Code to reproduce

```js
const superagent = require('superagent');

const r = superagent.get('https://www.google.com');
try {
r.set({ 'x-header': undefined }).end((err, result) => console.log('completed', err, result));
// r.set({ 'x-header': undefined }).then(result => console.log('completed', result)).catch(err => {
console.error('rejected', err);
// r.req.end();
});
} catch(e) {
console.log('caught', e);

// r.req.end();
}
```

This code snippet is a setup for two scenarios:

1. The current setup will use the `end()` syntax and when the error is caught, the application will hang for a few seconds and then exit.
2. If you uncomment the `r.req.end()` line inside the catch, the application will exit immediately.
3. If we comment out the first line inside the `try` block and uncomment the second line, we now are testing the `promise` based method. This also hangs before allowing the application to exit.
4. If we comment out the `r.req.end()` line inside the `.catch()` handler, then the application exits immediately.

## Checklist

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