Merge pull request matplotlib#26724 from meeseeksmachine/auto-backport-of-pr-26721-on-v3.8.x

Backport PR matplotlib#26721 on branch v3.8.x (Add a Python 3.12 classifier)

Author: QuLogic

setup.py

@@ -305,6 +305,7 @@ def make_release_tree(self, base_dir, files):
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',
+        'Programming Language :: Python :: 3.12',
         'Topic :: Scientific/Engineering :: Visualization',
     ],