Update `build-sdist` job

Follow on from #829

## The Issue
`build-sdist` does not generate any artifact.

The `actions/upload-artifact` step is looking to archive files in `target/wheels/*`, which `sdist` builds do not generate.

The generated archive from the logs ([reference job run](https://github.com/apache/datafusion-python/actions/runs/10501567861/job/29091775728)):

```console
Built source distribution to /home/runner/work/datafusion-python/datafusion-python/dist/datafusion-40.0.0.tar.gz
```

## Context
The release documentation currently expects only `wheels` to be included in `dist.zip` and for the `sdist` to be generated manually.

https://github.com/apache/datafusion-python/blob/805183bd9ae32b628e641d9552f1d0dded4a7a85/dev/release/README.md?plain=1#L142-L155

## Options

- Update the step to upload the tar archive as an artifact and update the release docs to use that.
- Update the step to assert that no wheels are generated in `target/wheels/*`, which will verify the sdist build and ensure the behavior doesn't change under our feet.
- Remove the step altogether.