fix: Add optional pr input and use gh api for complete PR data

[aaronsteers]

No description provided.

[Copilot]

Pull Request Overview

This PR enhances PR variable resolution by adding an optional pr input parameter and switching from GitHub CLI to GitHub API for more comprehensive PR data retrieval. The changes improve flexibility and data completeness when working with PR-related variables.

• Added optional pr input parameter to allow explicit PR specification, overriding auto-detection
• Switched from gh pr view to gh api for retrieving complete PR data including source/target details
• Added comprehensive PR-related variables including draft status, SHA values, and separate source/target variable sets

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
action.yml	Added pr input parameter and enhanced PR data fetching with GitHub API to populate comprehensive PR variables
.github/workflows/test-action.yml	Added workflow dispatch input for PR testing and configured action to use the new pr parameter

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