python: bump last remaining 3.8 to 3.9

note: Protobuf v31.0 has dropped support of Python 3.8

Author: Mizux

ortools/python/README.md

@@ -1,6 +1,6 @@
 # Introduction
 
-This is the documentation page for the Python 3.8+ wrapper of OR-Tools.
+This is the documentation page for the Python 3.9+ wrapper of OR-Tools.
 
 This project aim to explain how you build a Python native wheel package using
 [`setup.py`](https://packaging.python.org/tutorials/packaging-projects/).

ortools/python/setup.py.in

@@ -41,7 +41,7 @@ setup(
     name='@PYTHON_PROJECT@',
     version='@PROJECT_VERSION@',
     packages=find_packages(),
-    python_requires='>= 3.8',
+    python_requires='>= 3.9',
     install_requires=[
         'absl-py >= 2.0.0',
         'numpy >= 1.13.3',
@@ -159,7 +159,6 @@ setup(
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3 :: Only',
-        'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',