Policy Testing Workflow update - only test changed or added custom policies

[Springstone]

Overview/Summary

Policy Testing Workflow update - only test changed or added custom policies if a Pester test for that policy exists.

This PR fixes/adds/changes/removes

1. Updated portal testing workflow to only test changed or new policies

Breaking Changes

1. N/A

Testing Evidence

Testing URLs

Azure Public

As part of this Pull Request I have

• Checked for duplicate Pull Requests
• Associated it with relevant issues, for tracking and closure.
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Performed testing and provided evidence.
• Ensured contribution guidance is followed.
• Updated relevant and associated documentation.
• Updated the "What's New?" wiki page (located: /docs/wiki/whats-new.md)