ENH: Also test 2DImage.ipynb notebook in CI

Author: thewtex

.github/workflows/notebook-test.yml

@@ -14,4 +14,3 @@ jobs:
           docker-username: thewtex
           docker-password: "${{ secrets.DOCKER_PASSWORD }}"
           docker-image-name: insighttoolkit/itkwidgets
-          notebooks: "examples/3DImage.ipynb"

treebeard.yaml

@@ -0,0 +1,3 @@
+notebooks:
+    - examples/2DImage.ipynb
+    - examples/3DImage.ipynb