Use secret for dockerpublicbot username

Author: ColinMcNeil

.github/workflows/mcp_images.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:
-          username: dockerpublicbot
+          username: ${{ secrets.DOCKERPUBLICBOT_USERNAME }}
           password: ${{ secrets.DOCKERPUBLICBOT_WRITE_PAT }}
       - name: Build MCP Images
         run: |