ci: updated the credentials for building docker image

.github/workflows/build.yml

@@ -27,7 +27,7 @@ jobs:
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
-          password: ${{ secrets.RELEASE_TOKEN }}
+          password: ${{ secrets.GITHUB_TOKEN }}
       - name: Set Branch
         run: |
           export APPS_JSON='[{"url": "https://github.com/frappe/lms","branch": "main"}]'