Fix serve workflow to correctly install 'jupyter' dependency and update build command for HTML generation

.forgejo/workflows/serve.yaml

@@ -11,9 +11,11 @@ jobs:
       - name: Initialize virtual environment
         run: /usr/bin/python -m venv .env
       - name: Install dependencies
-        run: ./.env/bin/pip install mystmd jupyterlab jupyterlab_myst ipykernel altair pandas
+        run: ./.env/bin/pip install mystmd jupyter jupyterlab_myst ipykernel altair pandas
       - name: Build static HTML
-        run: ./.env/bin/myst build --execute --html
+        run: |
+          . .env/bin/activate
+          myst build --execute --html
       - name: Copy files
         run: |
           rm -rf /data/srv/forgejo-runner/cours4.0