DEV: Fail on Sphinx issues

.github/workflows/github-ci.yaml

@@ -164,6 +164,10 @@ jobs:
  - name: Test with mypy
  run : |
  mypy pypdf
+ - name: Test docs build
+ run: |
+ pip install -r requirements/docs.txt
+ sphinx-build -n -W --keep-going -T -b html docs build/sphinx/html
 
  package:
  name: Build & verify package