Update emscripten.yml

Author: mcbarton

.github/workflows/emscripten.yml

@@ -841,7 +841,7 @@ 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' }}
+      if: ${{ runner.os == 'macOS' && ${{ matrix.clang-runtime }} == '20' }}
       uses: rossjrw/pr-preview-action@v1
       with:
         source-dir: ./xeus-cpp/dist/