add python 3.11 to pypi metadata

setup.cfg

@@ -20,6 +20,7 @@ classifiers =
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
+    Programming Language :: Python :: 3.11
     Topic :: Security :: Cryptography
     Topic :: System :: Archiving :: Backup
 platforms = Linux, MacOS X, FreeBSD, OpenBSD, NetBSD