Fix module installation in PowerShell 3 and 4

[fflaten]

PR Summary

For some reason Install-Module for Pester 5.1.0+ fails on PowerShell 3 and 4 while testing the module manifest due to an error in a function that's never executed. Not worth figuring out why it's invoked, but fixing the invalid reference to the $SafeCommands-dictionary seems to fix it.

Fix #1791

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