Update oscal content so that it only runs on develop and main

[wandmagic]

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{Please provide a brief description of what this PR accomplishes. Be sure to reference any issues addressed. If the PR is a work-in-progress submitted for early review, please include [WIP] at the beginning of the title or mark the PR as DRAFT.}

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[wandmagic]

@iMichaela let me know once you have a chance to look at this

[david-waltermire]

This seems to be atypical for a continuous integration approach where the philosophy is to test that every commit is verified for correctness. Why not enable these validation checks to run on personal and feature branches to find issues early before they are merged into develop?

[iMichaela]

The PR is from March when @wandmagic was working on examples for the prototype models. The intention is to allow for development of content (examples) for the prototype models (not released) and not incorporated in the oscal-cli. We still have that need. With that said, I did not approve it because I wanted to take a different approach than the proposed one: to NOT run the tests and validations automatically on prototype-* branch but run on all others. I just did not have the cycle to get to it.