Pin moto

Using using moto 5.x lead to the following error:

```
from moto import mock_s3
E   ImportError: cannot import name 'mock_s3' from 'moto' (/home/klas/.venvs/py3117/lib/python3.11/site-packages/moto/__init__.py)
```

Installing with `moto[iam]<5` resolves this.