add newer python version builds

[river-walras]

This pull request updates the continuous integration workflow to use newer versions of Ubuntu and Python, and upgrades the GitHub Actions used for checking out code and setting up Python. These changes help ensure compatibility with the latest Python releases and improve CI reliability.

CI environment updates:

• Updated the build job to run on ubuntu-22.04 instead of ubuntu-20.04.
• Expanded the Python version matrix to include Python 3.11, 3.12, and 3.13, while dropping 3.6.

GitHub Actions upgrades:

• Upgraded actions/checkout from version 3 to 4.
• Upgraded actions/setup-python from version 3 to 5.

[Copilot]

Pull request overview

This pull request updates the CI workflow to support newer Python versions (3.11, 3.12, 3.13) and modernizes the testing infrastructure by upgrading to Ubuntu 22.04 and newer versions of GitHub Actions.

Changes:

• Upgraded CI environment from Ubuntu 20.04 to Ubuntu 22.04
• Expanded Python version matrix from 3.6-3.10 to 3.7-3.13 (dropping 3.6, adding 3.11, 3.12, 3.13)
• Updated GitHub Actions dependencies (checkout v3→v4, setup-python v3→v5)

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[Copilot]

Adding Python 3.11, 3.12, and 3.13 to the CI matrix requires updating the pybind11 dependency version in setup.py. The current minimum version (pybind11>=2.2) does not support these newer Python versions:

• Python 3.11 requires pybind11 2.10 or later
• Python 3.12 requires pybind11 2.11 or later
• Python 3.13 requires pybind11 2.12 or later

Without updating the pybind11 requirement, builds for Python 3.11+ will fail during compilation. Consider updating setup.py to require pybind11>=2.12 to support the entire version range being tested.

Suggested change

	python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13']
	python-version: ['3.7', '3.8', '3.9', '3.10']