Add 3.12 to PyPI metadata

Author: simonw

setup.py

@@ -77,6 +77,7 @@ def get_long_description():
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
+        "Programming Language :: Python :: 3.12",
     ],
     # Needed to bundle py.typed so mypy can see it:
     zip_safe=False,