package metadata: add python3.10 classifier

tests enabled in https://github.com/fphammerle/tooncher/commit/5099ae1500704c7617023a78964b8c49ad277d76#diff-092659a9bd0068791326fb1d08f005532e5aeb983b999a7bd32c51deee0a71d5R41

setup.py

@@ -24,6 +24,7 @@ setuptools.setup(
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Topic :: Games/Entertainment",
         "Topic :: Utilities",
     ],