Add test line to build-system README for PR workflow verification

[Komali0706]

This pull request adds a small, non-impactful test line to the end of the
build-system/README.md file.

The purpose of this change is to verify that the full fork → branch → commit →
pull request → merge workflow is working correctly. This update does not alter
any functionality, build behavior, or project logic. It is only intended to
confirm that pull requests can be created and merged successfully.

[CLAassistant]

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