Python: Fix set-env not allow in workflow (#9973)

### Motivation and Context

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`set-env` command is disabled in our workflow.

![image](https://github.com/user-attachments/assets/a6813291-e58f-4691-ae05-efd35c04ec15)

### Description

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Use `$GITHUB_ENV` instead.

### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
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raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Co-authored-by: Evan Mattson <[email protected]>

.github/workflows/python-test-coverage-report.yml

@@ -32,7 +32,7 @@ jobs:
         run: |
           PR_NUMBER=$(cat pr_number)
           echo "PR number: $PR_NUMBER"
-          echo "::set-env name=PR_NUMBER::$PR_NUMBER"
+          echo "PR_NUMBER=$PR_NUMBER" >> $GITHUB_ENV
       - name: Pytest coverage comment
         id: coverageComment
         uses: MishaKav/pytest-coverage-comment@main