3.0 Deprecation Warning: Convert warning into exception in `rasa.shared.utils.common.py`

**Background**
This warning was found in `rasa.shared.utils.common.py:L48`
```
"f""`class_from_module_path()` is expected to return a class, ""
f""but {module_path} is not one. ""
f""This warning will be converted ""
f""into an exception in {NEXT_MAJOR_VERSION_FOR_DEPRECATIONS}."""
```

**Definition of Done**
- [ ] resolve warning in 3.0