req.session is not available with Fastify

During development (with `sandbox`) everything works, but when I would like to deploy with `Fastify`, the `req.session` is not available.

```
"statusCode": 500,
"error": "Internal Server Error",
"message": "Cannot destructure property '_idx' of 'req.session' as it is undefined."
}
```

Reproduce:
- Clone [this](https://github.com/andrasbacsai/enhancedev-fastify) repository.
- `pnpm install`
- Test if it's working with `pnpm dev` -> Yes it will.
- Test if it's working with `pnpm start` -> Nope.

Let me know if you need any further information.