Add PostProcessing to editor test copy step

Seems needed to succeed

build.py

     copy_path_to_project("SampleScenes", repo_path, project_path, logger)
     copy_path_to_project("TestbedPipelines", repo_path, project_path, logger)
     copy_path_to_project("Tests", repo_path, project_path, logger)
+    # Temporary until post processing handled properly
+    copy_path_to_project("PostProcessing", repo_path, project_path, logger)