make doc fails when hitting warnings

https://stackoverflow.com/questions/38048945/how-to-turn-warnings-into-errors-when-building-sphinx-documentation-with-setupto

.github/workflows/build_docs.yml

@@ -31,7 +31,7 @@ jobs:
     - name: Test building docs & Archive the results
       run: |
         cd docs
-        make html
+        make html SPHINXOPTS="-W --keep-going -n"
         ls build/html
         tar czf docs.tar.gz --directory=build/html .
         cd ..