Update emscripten.yml

Author: mcbarton

.github/workflows/emscripten.yml

@@ -9,6 +9,10 @@ on:
   schedule:
     - cron: '30 20 * * *' # Warning: Timezone dep - 20:00 is 1:00
 
+permissions:
+  contents: read
+  pull-requests: write
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
   cancel-in-progress: true
@@ -841,7 +845,7 @@ jobs:
           jupyter lite build --XeusAddon.prefix=${{ env.PREFIX }} --contents notebooks/xeus-cpp-lite-demo.ipynb --contents notebooks/smallpt.ipynb --contents notebooks/images/marie.png --contents notebooks/audio/audio.wav --output-dir dist
 
     - name: Deploy preview
-      if: ${{ runner.os == 'macOS' && matrix.clang-runtime == '20' }}
+      if: ${{ runner.os == 'macOS' && matrix.clang-runtime == '20' && github.event_name == 'pull_request' }}
       uses: rossjrw/pr-preview-action@v1
       with:
         source-dir: ./xeus-cpp/dist/