Add check to PR action

.github/workflows/pull_request.yaml

@@ -53,3 +53,13 @@ jobs:
         run: pytest
       - name: Test documentation builds
         run: make documentation
+
+      - name: Check documentation build
+        run: |
+          for notebook in $(find docs/_build/jupyter_execute -name "*.ipynb"); do
+            if grep -q '"output_type": "error"' "$notebook"; then
+              echo "Error found in $notebook"
+              cat "$notebook"
+              exit 1
+            fi
+          done