Added 3.13 classifier (#322)

Author: edgarrmondragon

setup.py

@@ -56,6 +56,7 @@
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",
+        "Programming Language :: Python :: 3.13",
     ],
     project_urls={
         "Source": "https://github.com/certifi/python-certifi",