Summary
Improve "Duplicate Packages Samples" CI workflow to read {srcPath:destPath} pairs from file inside the repository instead of repository variables.

Suggested features or ways to address the summary
Create a new text file (suggested path & name: ".github/duplicate-samples-list.txt") with a simple format like so:

{src/UnitySampleProject/Assets/Samples/$PackageDisplayName$Sample:Packages/$PackageName$/Samples~/$PackageDisplayName$/}
{...:...}
...

Make the CI workflow read values from this file instead of repository variables.

Motivation
This would fix the issue when you're adding a new entry to the list of {src:dest} pairs, but those paths don't yet exist in other branches.

Acceptance Criteria
We're using values from the file from the branch instead of repository settings. Everything else works as it was before.