fix: remove trailing slash when uploading to S3 with dataset_builder.to_csv_file

[mkkatica]

Issue #, if available: #4569

Description of changes: Use rstrip to remove trailing slash when uploading the temp file to s3 during dataset creation.

Testing done: Installed the modified version and ran the code that was previously failing

Merge Checklist

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• I have read the CONTRIBUTING doc
• I certify that the changes I am introducing will be backward compatible, and I have discussed concerns about this, if any, with the Python SDK team
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• I have passed the region in to all S3 and STS clients that I've initialized as part of this change.
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Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[mkkatica]

Are there any existing tests for DatasetBuilder.to_csv_file()? I couldn't find any in tests/integ/sagemaker/feature_store.