new python final release checklist

update the max version supported in setup-cfg-fmt

for example this PR

regenerate symbols in flake8-typing-imports

for example this PR

regenerate reorder-python-imports symbols

for example this PR

regenerate pyupgrade symbols

for example this PR

replace backports where necessary

for example, importlib-metadata in python3.8

update github actions workflows

for example this PR

update pre-commit.ci pythons

for example this PR

and then 3 months later, update the default version to that