Update documentation.yml

maybe this one liner?

.github/workflows/documentation.yml

@@ -17,7 +17,8 @@ jobs:
           #pip install sphinx renku-sphinx-theme sphinx-rtd-theme
           #pip install renku-sphinx-theme
           #pip install --upgrade sphinx-rtd-theme
-          pip install --upgrade sphinx sphinx-rtd-theme
+          #pip install --upgrade sphinx sphinx-rtd-theme
+          pip install --upgrade sphinx renku-sphinx-theme sphinx-rtd-theme          
       - name: Sphinx build
         run: |
           sphinx-build docs build