Fix missing jupyter-packaging

Author: fcollonval

.github/workflows/main.yml

@@ -261,7 +261,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-pip-
       - name: Install the Python dependencies
-        run: python -m pip install jupyterlab~=3.0 pytest pytest-check-links
+        run: python -m pip install jupyter_packaging~=0.7.9 jupyterlab~=3.0 pytest pytest-check-links
       - name: Bootstrap the jlpm deps
         run: jlpm
       - name: Build all the extensions