GraphqlError - The "extensions" property can be undefined and lead to unwanted behavior
### Issue
When you use internal errors within your service and you want to use [the powerful `formatError` hook to remap the errors into Graphql's one](https://www.apollographql.com/docs/apollo-server/data/errors/#custom-errors), it actually, this lead to an error see above.

```
Unexpected Error Cannot read properties of undefined (reading 'code')
```

### Resolution
https://github.com/apollographql/apollo-server/blob/268687db591fed8293eeded1546ae2f8e6f2b6a7/packages/server/src/errorNormalize.ts#L64C8-L64C37

```
graphqlError.extensions?.code
```