Bump version to 0.7.4

[snarayan21]

Description of changes:

bumps version to 0.7.4

Issue #, if available:

Merge Checklist:

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General

• I have read the contributor guidelines
• This is a documentation change or typo fix. If so, skip the rest of this checklist.
• I certify that the changes I am introducing will be backward compatible, and I have discussed concerns about this, if any, with the MosaicML team.
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Tests

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