SQL Job Agent Service Account - Access is denied to run Powershell
You have to call powershell.exe instead of the foldername

Change this

"C:\Windows\System32\WindowsPowerShell\v1.0" "C:\test\testscript.ps1"


To this

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" "C:\test\testscript.ps1"


Testing by creating the same jobstep



The original command

"C:\Windows\System32\WindowsPowerShell\v1.0" "C:\test\testscript.ps1"


The error 


  Executed as user: ServiceAcc. The process could not be created for
  step 1 of job .. (reason: Access is denied).  The step failed.


Changing the command and running the job again

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" "C:\test\testscript.ps1"


Great success