Upgrade Python to 3.12.6 #110
Description
Python 3.12 is being used for a fair number of libraries and staying on Python 3.12 breaks builds that require packages of only 3.11 and down.
This (#109) draft PR starts the process, though it will be a fair bit of work to upgrade serious-python and all other related dependencies to Python 3.12.
I picked Python 3.12.6 because it's the latest build right now and some of the referenced dependencies in the PR already support it.
See this issue for an example of the type feature in 3.12 that someone wants to use in Flet that would be enabled by this upgrade.
This may fix the following issue: flet-dev/flet#4007