Update Classifiers (#15259)

Author: Rakshith Bhyravabhotla

sdk/eventgrid/azure-eventgrid/setup.py

@@ -70,6 +70,7 @@
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'License :: OSI Approved :: MIT License',
     ],
     zip_safe=False,