add ase package for testing

Author: Dou Du

.github/workflows/screenshot-comparison.yml

@@ -30,6 +30,7 @@ jobs:
         pip install --upgrade jupyterlab
         pip install --upgrade voila
         pip install --upgrade voila-osscar-template
+        pip install --upgrade ase
         pip install -e .
 
     - name: Run the voila server

.github/workflows/widget-test.yml

@@ -30,6 +30,7 @@ jobs:
         pip install --upgrade jupyterlab
         pip install --upgrade voila
         pip install --upgrade voila-osscar-template
+        pip install --upgrade ase
         pip install -e .
 
     - name: Run the voila server