Opening a template that has Post Processing stack gives "Permission denied" and "Fatal error!" messages while trying to launch the Unity editor. The error prevents Unity editor to be launched successfully. The issue only occurs on Mac platform and deleting the cache doesn't resolve the issue on my machine.

In addition, this problem only occurs when trying to fetch the package for the first time. After the failure, Unity editor can successfully load and open the downloaded project without a problem.

Steps for reproduction:
1) Download a mac build from "2018.1/templates/package-updates-and-new-content" branch
2) Choose one of the templates that has Post Processing stack (i.e. 3D Extras, HDRP, LW, LW VR)
3) Observe the errors that appear when downloading process is done (details are shared below in comments section)