(fix) ModulesDir blank when invoked as quicklink

[JPRuskin]

Description Of Changes

Fixes a usage of PSScriptRoot in the initializing script.

Motivation and Context

The script was failing to run when it hadn't been run from disk, e.g. when using the irm qsg-go | iex method. This wasn't caught by the tests because we download and run it from disk in those scripts, but we often enjoy using the easier to remember method above.

Testing

1. Tested on a local Windows Server 2022 VM by running with the raw URL from my branch, rather than the short link.

Operating Systems Testing

• Windows 2022

Change Types Made

• [x] Bug fix (non-breaking change).
• ~[ ] Feature / Enhancement (non-breaking change).~
• ~[ ] Breaking change (fix or feature that could cause existing functionality to change).~
• ~[ ] Documentation changes.~
• [x] PowerShell code changes.

Change Checklist

• ~[ ] Requires a change to the documentation.~
• ~[ ] Documentation has been updated.~
• ~[ ] Tests to cover my changes, have been added.~
• [x] All new and existing tests passed?
• [x] PowerShell code changes: PowerShell v3 compatibility checked?