Add support for Python 3.12 and drop EOL 3.7

[hugovk]

The final Python 3.12 release candidate is out! 🚀

Call to action

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.12 compatibilities during this phase, and where necessary publish Python 3.12 wheels on PyPI to be ready for the final release of 3.12.0.

Python 3.12.0 final is due out on Monday: 2023-10-02.

See also https://dev.to/hugovk/help-test-python-312-beta-1508/

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Python 3.7 is EOL and no longer receiving security updates (or any updates) from the core Python team.

version	released	eol
3.11	2022-10-24	2027-10-24
3.10	2021-10-04	2026-10-04
3.9	2020-10-05	2025-10-05
3.8	2019-10-14	2024-10-14
3.7	2018-06-26	2023-06-27

https://devguide.python.org/versions/

And remove the old Travis CI, it's no longer used and GitHub Actions is used for CI.