Fix CI require beam
This PR:
- Fixes the CI `require_beam`: before it was requiring PyTorch instead
  ```python
  def require_beam(test_case):
      if not config.TORCH_AVAILABLE:
          test_case = unittest.skip("test requires PyTorch")(test_case)
      return test_case
  ```
- Fixes a missing `require_beam` in `test_beam_based_builder_download_and_prepare_as_parquet`
- Refactors `require_beam` to use `pytest` (`skipif`) instead