Add Python 3.12 classifier (#12019)

Author: pradyunsg

setup.py

@@ -42,6 +42,7 @@ def get_version(rel_path: str) -> str:
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
+        "Programming Language :: Python :: 3.12",
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy",
     ],