Add 3.13 to trove classifiers (#72)

Since 3.13 is part of the CI, it's fair to call it supported.

Author: hynek

setup.py

@@ -239,6 +239,7 @@ def has_ext_modules(self):
             'Programming Language :: Python :: 3.10',
             'Programming Language :: Python :: 3.11',
             'Programming Language :: Python :: 3.12',
+            'Programming Language :: Python :: 3.13',
             'Programming Language :: Python :: Implementation :: CPython',
             'Programming Language :: Python :: Implementation :: PyPy',
             'License :: OSI Approved :: MIT License',