ci: bump CI to Python 3.11 and refresh deprecated action versions #787

CI pins Python 3.8 and three GitHub Actions that are several major versions behind.

Python 3.8 reached end-of-life on 2024-10-07 and no longer receives security fixes. actions/checkout@v3, actions/setup-python@v4, and actions/setup-node@v3 rely on Node.js 16, which GitHub deprecated and started warning about across all repos.

Affected files

• .github/workflows/lint-check.yml:14 actions/checkout@v3
• .github/workflows/lint-check.yml:17-19 actions/setup-python@v4, python-version "3.8"
• .github/workflows/lint-check.yml:22 actions/setup-node@v3
• .github/workflows/integration-tests.yml:14 actions/checkout@v3
• src/api-engine/tox.ini:8 envlist = py38, flake8
• src/api-engine/tox.ini:26-27 [gh-actions] python = 3.8: py38, flake8

Proposal

• Python 3.8 -> 3.11 (supported on ubuntu-latest, current upstream stable).
• actions/checkout@v3 -> v4
• actions/setup-python@v4 -> v5
• actions/setup-node@v3 -> v4
• tox envlist and [gh-actions] map updated to py311.

Happy to file the PR in parallel. Will adjust if maintainers prefer 3.10 or a wider matrix.