Test jupyter_client dev version

Author: davidbrochart

.github/workflows/downstream.yml

@@ -23,7 +23,9 @@ jobs:
         run: |
           pip install --upgrade pip
           pip install .
-          pip install pytest nbclient[test] ipyparallel[test] jupyter_client[test] pytest-asyncio
+          pip install pytest nbclient[test] ipyparallel[test] \
+                             "jupyter_client[test] @ git+git://github.com/jupyter/jupyter_client.git@master" \
+                             pytest-asyncio
           pip freeze
 
       - name: Run tests