Bump Python version to Python 3.12.6

[kentbull]

This is a draft PR to start the process of building in support for Python 3.12.6. There appears to be a fair bit of work involved to make this happen in a number of different dependent repos, so this may remain WIP for a while.

• python-build-standalone supports python 3.12.6 as of release https://github.com/indygreg/python-build-standalone/releases/tag/20240909
• Beeware's Python-Apple-support supports python 3.12.6 as of release https://github.com/beeware/Python-Apple-support/releases/tag/3.12-b4
• Kivy iOS needs PR to update to 3.12.6. See this example PR
  • PR in progress here: kivy-ios#941
• Kivy Android needs PR to update to 3.12.6. See this example PR
  • PR in progress here: python-for-android#1

Fixes #110

Should fix flet-dev/flet#4007

[FeodorFitsner]

Thanks for your PR! Really appreciate the efforts you put into it!

Fortunately, we are in the process of releasing packaging "v2" (https://github.com/flet-dev/serious-python/tree/packaging-v2) which is not just based on 3.12.6, but it does not use/depend on Kivy anymore. The new packaging is going to be ready next week, so you safely close this PR. 🙌

[kentbull]

Woot, woot! Hooray! That is awesome and I look forward to using the v2 release packaging. Thanks! I'll close this PR.

[torablien]

The new packaging is going to be ready next week

Very excited to try this!

[kentbull]

I'm glad to test anything out and provide early feedback on packaging-v2.