Update action.yml

Author: mcbarton

.github/actions/Emscripten-Notebook-Tests/action.yml

@@ -80,6 +80,7 @@ runs:
         fi
         # Kill the jupyter lite serve process now we are done running xeus-cpp in the
         # Jupyter Lite website.
+        pstree -p $jupyter_lite_process_id
         kill -9 $jupyter_lite_process_id
         sleep 10
         ps