Add checkpoint BC tests for 0.27.0 and 0.28.0

[snarayan21]

What does this PR do?

As title. Adds for 0.27.0 as well since this was not done upon release.

Daily tests passed: https://github.com/mosaicml/composer/actions/runs/12184347841

What issue(s) does this change relate to?

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[j316chuck]

Thank you for patching 0.27.0 ❤️