utils.pwsh: Fix Windows config paths

[RytoEX]

Description

Apparently, CMake can fail when parsing the current path string because it interprets the backslash as the start of an escape sequence. Modern Windows can interpret paths with forward slashes, so it should be safe to change these slashes.

Motivation and Context

Discovered this while attempting to update dependencies. Want to fix it separate from that update.

https://github.com/RytoEX/obs-deps/actions/runs/23963204885/job/69897580516#step:4:6211

How Has This Been Tested?

I haven't tested this change yet, but we use forward slashes in other paths for Windows elsewhere, so this is hopefully fine.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.