fix: correct GitHub Actions job status variable usage in PR validation

- Fix incorrect usage of process.env.GITHUB_JOB_STATUS (doesn't exist)
- Use ${{ job.status }} directly as intended in github-script action
- Resolves potential undefined variable issue in comment generation
- Ensures proper success/failure status detection for PR comments

This fix addresses a JavaScript runtime error in the comment generation step
where an undefined environment variable was being used as fallback.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: minipuft

.github/workflows/pr-validation.yml

@@ -183,7 +183,7 @@ jobs:
               console.log(`Warning: Could not read changed_files.txt: ${e.message}`);
               changedFiles = 'Unable to read changed files (this is normal for some PR types)';
             }
-            const status = process.env.GITHUB_JOB_STATUS || '${{ job.status }}';
+            const status = '${{ job.status }}';
             const runUrl = `${context.payload.repository.html_url}/actions/runs/${context.runId}`;
             let message;
             if (status === 'success') {