fix: remove unused SHORT_SHA variable from update-readme step

Agent-Logs-Url: https://github.com/luke-b/DosTest/sessions/50fde0f7-fd08-4ca9-8a43-7a44b4932b85

Co-authored-by: luke-b <1448891+luke-b@users.noreply.github.com>

Author: Copilot

.github/workflows/borland-dos-pipeline.yml

@@ -225,7 +225,6 @@ jobs:
 
       - name: Update demo link in README.md
         run: |
-          SHORT_SHA="${{ steps.sha.outputs.short }}"
           DEMO_URL="https://luke-b.github.io/DosTest/demo/build/latest/"
           BADGE_LINE="[![Play latest build](https://img.shields.io/badge/Play-Latest%20Build-brightgreen)](${DEMO_URL})"
           BLOCK="<!-- DEMO_LINK -->\n${BADGE_LINE}\n<!-- /DEMO_LINK -->"