Error from resolver without extensions[V3 was not adding extensions in any error type from resolvers]
### Issue Description

While migrating from V3 to V4, we haven't changed any code in datasources as migration doc suggest no real changes are required.

Once we upgraded to V4, one of our resolvers throws an error(Normal HTTP error of timeout request). We started receiving following error.
```
{
  "data": {},
  "errors": [
    {
      "message": "Internal server error",
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR"
      }
    }
  ]
}
```

Upon debugging we identified the following issue, where error is in "errorNormalize.ts" file where function enrichError has following condition which causes following error.

```
    const extensions: GraphQLErrorExtensions = {
      ...graphqlError.extensions,
      code:
        graphqlError.extensions.code ??
        ApolloServerErrorCode.INTERNAL_SERVER_ERROR,
    };
```
`Error: "code" of undefined`, where extensions does not exists on error.

I would recommend to either add `graphqlError.extensions.code` with `graphqlError.extensions?.code` or in `ensureGraphQLError` function add extensions if error does not has those fields.





### Link to Reproduction

https://codesandbox.io/p/sandbox/funny-haibt-s4r82s?file=%2Fsrc%2Findex.ts%3A34%2C14

### Reproduction Steps

Note: Somehow above code is not working while it does work on my local machine and as explained in above description we are facing this issue.