fix: Unpin cloudpickle

[speller26]

aws/sagemaker-python-sdk#4871 has been resolved

Issue #, if available:

Description of changes:

Testing done:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8019e5a) to head (360a583).

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files          171       171           
  Lines        11648     11648           
  Branches      1538      1538           
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  Hits         11648     11648           

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[rmshaffer]

This change becomes tricky because cloudpickle explicitly doesn't support serializing with one version and deserializing with a different version. If we unpin it, we create the possibility of mismatched versions between a user's client (wherever they are running their code with the @hybrid_job decorator), and the hybrid job container where it runs.

For a specific example: after the job container upgrades to an SDK version with this change, it will get the latest cloudpickle version (3.x), but users of older SDK versions or with older environments will be using old cloudpickle (2.x). This is not guaranteed to work (and in practice we've seen that it often doesn't).

Is there a reason that we truly want/need a newer cloudpickle version? If so, we need to somehow safeguard against the above scenario.