CI: Temporarily disable treating warnings as errors

.github/workflows/ci.yml

@@ -26,4 +26,4 @@ jobs:
       # Use dummy builder to improve performance as we don't need the generated HTML in this workflow.
       - name: Sphinx build
         run: |
-          sphinx-build --color -b dummy -d _build/doctrees -W . _build/html
+          sphinx-build --color -b dummy -d _build/doctrees . _build/html