add test for explicit PR number

[aaronsteers]

No description provided.

[Copilot]

Pull Request Overview

This PR adds a test for explicit PR number functionality to the CI/CD workflow. The changes restructure the existing workflow to combine test jobs and add a new test case that explicitly sets a PR number.

• Removes the separate test-standard-ci-vars job and moves its functionality into the existing test job
• Adds comprehensive verification steps for standard CI variables
• Introduces a new test case that uses an explicit PR number (5) in the action configuration

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