setup.py: Add Python 3.10

Author: juergbi

setup.py

@@ -327,6 +327,7 @@ def files_from_module(modname):
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Topic :: Software Development :: Build Tools",
     ],
     description="A framework for modelling build pipelines in YAML",