Declare support for Python 3.9 in the metadata

Co-authored-by: Rick Elrod <rick@elrod.me>

changelogs/fragments/setup-py-declare-py39.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - setup.py - Declare that Python 3.9 is now supported (https://github.com/ansible/ansible/pull/72861).

setup.py

@@ -390,6 +390,7 @@ static_setup_params = dict(
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'Topic :: System :: Installation/Setup',
         'Topic :: System :: Systems Administration',
         'Topic :: Utilities',