Fix publish release workflow

Author: martenrichter

.github/workflows/publish-release.yml

@@ -22,6 +22,12 @@ jobs:
     steps:
       - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
 
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ vars.APP_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
+
       - name: Populate Release
         id: populate-release
         uses: jupyter-server/jupyter_releaser/.github/actions/populate-release@v2