🔧 (build-sandbox-image.yml): update npm token secret from GITHUB_TOKEN to NPM_TOKEN for correct authentication

Author: nsosio

.github/workflows/build-sandbox-image.yml

@@ -58,7 +58,7 @@ jobs:
             KOSUKE_CLI_MODE=production
             INSTALL_CHROMIUM=false
           secrets: |
-            npm_token=${{ secrets.GITHUB_TOKEN }}
+            npm_token=${{ secrets.NPM_TOKEN }}
 
       - name: Notify Slack - Success
         if: success()