Use Python 3.9 on Windows

[Starz0r]

Currently GitHub generates executables for Windows from Python 3.8, which has been EOL for more than 2 months now. This PR corrects it by building with Python 3.9 instead of an out of date Python.

[mikf]

The windows_x86.exe executables are meant for backwards compatibility. I'd like to keep them usable on Windows 7 machines, so (regular) Python 3.8 is the highest this can go.

[Starz0r]

I don't think it's worth supporting a version of Windows that old. Even so, the current (Windows) binaries on GitHub are built with CPython 3.8, and there isn't a distinguished x86 or x64 build. Just a singular x64 build that uses CPython 3.8. Is it possible that we can get binaries that are built with CPython 3.9 support?

[mikf]

The GitHub Actions workflow this PR is modifying is responsible for building and releasing "nightly" binaries at https://github.com/gdl-org/builds/releases

The stable releases from https://github.com/mikf/gallery-dl/releases are built on my own PC on a Windows 7 x86 VM and a Ubuntu 22.04 LTS VM as a part of running scripts/release.sh

[amayra]

is there any benefit of upgrading Python that is used for building if you don't use any new features in the newest versions?

[mikf]

CPython interpreters got faster / more efficient with each new version, especially Python 3.11. There are probably security related bug fixes that do not get ported to the EOL versions.