Dropping support for Python 3.8

[Avasam]

CPython 3.8 is EOL as of October 7 2024.
Anaconda has dropped support at the end of October.
CPython 3.9 is EOL as of October 2025.

Highlights represented by these changes:

• PEP 584, union operators added to dict;
• PEP 585, type hinting generics in standard collections;
• PEP 616, string methods to remove prefixes and suffixes.
• PEP 593, flexible function and variable annotations;
• PEP 617, Parenthesized context managers (this is a Python 3.9 change despite being listed under Python 3.10)
• https://www.nuget.org/packages/pythonarm64 had no download for Python 3.8
• Unconditional setuptools lower pin (see [BUG] v76.1.0 broke pywin32 builds pypa/setuptools#4968 and Fix setuptools 76.1 issue (and bump to >=77.0.3) #2587)
• Python 3.8 was also the last CPython version to offer out of the box support for Windows 7 / Windows Server 2008 (which are EOL since January 14, 2020)
  • It doesn't seem this could lead to any code simplification in the current codebase. So I left this simply as a note in the changelog. Users could continue to use pywin32 on Windows 7 by using special, unofficial Python build.
• Various deprecations

Additional points of interest from dropping Python 3.8 (not done in this PR):

• We now have unconditional access to the zoneinfo module: https://docs.python.org/3/whatsnew/3.9.html#zoneinfo, which may or may not be usable as part of win32/Lib/win32timezone.py.
• pip 25.1 dropped support for Python 3.8 and added a --group option supporting PEP 735 – Dependency Groups in pyproject.toml. Which would allow pywin32 to declare its dev dependencies in pyproject.toml without duplicating them in .github/workflows/main.yml and without exposing dev-only extras.
  Read more here: https://ichard26.github.io/blog/2025/04/whats-new-in-pip-25.1/#dependency-groups-pep-735
  • Done in Declare dev dependencies using PEP 735 – Dependency Groups in pyproject.toml #2672