Error when trying to run feast with local provider and duckdb as offline store

## Expected Behavior

When I try to run the `python test_workflow.py` of the quickstart with duckdb as the offline store, it should run without issues. The `feature_store.yaml` is configured as in the following example

```yaml
project: my_local_fs_with_db
registry: data/registry.db
provider: local
offline_store:
type: duckdb
online_store:
type: sqlite
path: data/online_store.db
entity_key_serialization_version: 2
```

And I have a virtual environment with

```
feast[duckdb]
duckdb
pandas
ibis-framework[duckdb]
```

## Current Behavior

However, I got the following error

```
Traceback (most recent call last):
File "/home/carrefour/Desktop/playground/feature-store/feast/my_local_fs_with_db/feature_repo/test_workflow.py", line 130, in
run_demo()
File "/home/carrefour/Desktop/playground/feature-store/feast/my_local_fs_with_db/feature_repo/test_workflow.py", line 16, in run_demo
fetch_historical_features_entity_df(store, for_batch_scoring=False)
File "/home/carrefour/Desktop/playground/feature-store/feast/my_local_fs_with_db/feature_repo/test_workflow.py", line 86, in fetch_historical_features_entity_df
training_df = store.get_historical_features(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/carrefour/Desktop/playground/feature-store/feast/.venv/lib/python3.12/site-packages/feast/feature_store.py", line 1161, in get_historical_features
job = provider.get_historical_features(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/carrefour/Desktop/playground/feature-store/feast/.venv/lib/python3.12/site-packages/feast/infra/passthrough_provider.py", line 459, in get_historical_features
job = self.offline_store.get_historical_features(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/carrefour/Desktop/playground/feature-store/feast/.venv/lib/python3.12/site-packages/feast/infra/offline_stores/duckdb.py", line 161, in get_historical_features
return get_historical_features_ibis(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/carrefour/Desktop/playground/feature-store/feast/.venv/lib/python3.12/site-packages/feast/infra/offline_stores/ibis.py", line 230, in get_historical_features_ibis
read_fv(feature_view, feature_refs, full_feature_names)
File "/home/carrefour/Desktop/playground/feature-store/feast/.venv/lib/python3.12/site-packages/feast/infra/offline_stores/ibis.py", line 192, in read_fv
fv_table = fv_table.mutate(
^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'mutate'
```

## Steps to reproduce

Run the example of the quickstart with `duckdb` as the offline store, as shown above.

### Specifications

- Version:
- Platform:
- Subsystem:

## Possible Solution

This seems to happen because the `_read_data_source` of the `offline_stores/duckdb.py` tries to determine the file_format by comparing the `data_source.file_format` but its value is None and therefor the `_read_data_source` also returns None, causing the AttributeError described earlier. A possible solution would be to certify that the `file_format` of a data source object always has a valid value.