fix: Removed version hardcoding for sagemaker test dependency

Issue #, if available: N/A

Description of changes: Hardcoding the older version of the sagemaker-python-sdk required additional IAM policies to be able to access the default sagemaker bucket in tests. This change removes the hardcoding so that tests can be run with the most recent sagemaker version

Testing done: Re-confirmed using tox -e py38 -- test/functional

Merge Checklist

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General

[ x] I have read the CONTRIBUTING doc
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[x ] I have updated any necessary documentation, including READMEs

Tests

[x ] I have added tests that prove my fix is effective or that my feature works (if appropriate)
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aws / sagemaker-training-toolkit