AWS callback warning

In my AWS logs for a S3 Bucket notification lambda that uses serverless-express, I get the following warning:

```
AWS Lambda plans to remove support for callback-based function handlers starting with Node.js 24. You will need to update this function to use an async handler to use Node.js 24 or later. For more information and to provide feedback on this change, see https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/137. To disable this warning, set the AWS_LAMBDA_NODEJS_DISABLE_CALLBACK_WARNING environment variable.
```

This is how I'm creating the request handler:

```
export const handler = serverlessExpress({
app,
eventSourceRoutes: {
AWS_S3: "/s3",
},
});
```

Seems like serverless-express may need some internal update to be compatible with the new AWS updates?

Edit>> My version is `4.16.0`

Start from the serverlessExpress({ app, eventSourceRoutes: { AWS_S3: "/s3" } }) entry point and inspect how the Lambda handler is created. Reproduce the warning with the reported version, 4.16.0, and determine the compatibility change needed for Node.js 24. Done means the S3 notification handler no longer triggers AWS's callback-based handler warning while retaining its routing behavior.

索引モデルが issue の本文から書いたものです。