Add Python 3.12 classifier

Author: matt-graham

pyproject.toml

@@ -18,6 +18,7 @@ classifiers = [
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
     "Operating System :: OS Independent",
     "Intended Audience :: Developers",
     "Intended Audience :: Science/Research",