Add PostProcessing package to build list

build.py

         ("com.unity.render-pipelines.lightweight", os.path.join("com.unity.render-pipelines.lightweight")),
         ("com.unity.render-pipelines.high-definition", os.path.join("com.unity.render-pipelines.high-definition")),
         ("com.unity.shadergraph", os.path.join("com.unity.shadergraph")),
+        ("com.unity.postprocessing", os.path.join("com.unity.postprocessing")),
     ]
 
 def test_packages_list():
         "com.unity.render-pipelines.high-definition",
-        "com.unity.shadergraph"
+        "com.unity.shadergraph",
+        "com.unity.postprocessing"
     ]
 
 if __name__ == "__main__":