[WIP] Update Python version in CI workflow file

[Copilot]

• Update Python version in CI.yml matrix strategy (line 18): change 3.7 to 3.9 (also removed 3.7 from matrix)
• Update Python version in CI.yml coveralls job (line 64): change 3.7 to 3.9
• Update Python version in CD.yml release job (line 26): change 3.7 to 3.9
• Verify all changes are correct

Original prompt

The CI job is failing because Python 3.7 is no longer available on the GitHub Actions runner. Update the workflow file at .github/workflows/CI.yml to use a supported Python version (e.g., 3.9) instead of 3.7.

Find the following section in the workflow file:

    - uses: actions/setup-python@v2
      with:
        python-version: '3.7'

Replace it with:

    - uses: actions/setup-python@v2
      with:
        python-version: '3.9'

This change ensures the workflow uses a Python version available on GitHub Actions, resolving the job failure.

This pull request was created from Copilot chat.

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