Refactor has-oscal-namespace to use @nspredicate filter

[aj-stein-gsa]

Committer Notes

Closes #2113.

All Submissions:

• Have you selected the correct base branch per Contributing guidance?
• Have you set "Allow edits and access to secrets by maintainers"?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you squashed any non-relevant commits and commit messages? [instructions]
• Do all automated CI/CD checks pass?

By submitting a pull request, you are agreeing to provide this contribution under the CC0 1.0 Universal public domain dedication.

(For reviewers: The wiki has guidance on code review and overall issue review for completeness.)

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you included examples of how to use your new feature(s)?
• Have you updated the OSCAL website and readme documentation affected by the changes you made? Changes to the OSCAL website can be made in the OSCAL-Pages and OSCAL_Reference repositories.