Fix CI require beam

[albertvillanova]

This PR:

• Fixes the CI require_beam: before it was requiring PyTorch instead

  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

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[albertvillanova]

I'm merging this PR because it is quite a trivial fix and this is required by:

• Support dill 0.3.6 #5166