Updating Setup.py with support py39.

PiperOrigin-RevId: 440444779

Author: tf-transform-team

setup.py

@@ -84,6 +84,7 @@ def _make_required_install_packages():
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3 :: Only',
         'Topic :: Scientific/Engineering',
         'Topic :: Scientific/Engineering :: Artificial Intelligence',