Pin Pygments below 2.20 to unbreak mkdocs build

[nicoloesch]

https://github.com/AustralianCancerDataNetwork/orm-loader/actions/runs/30783414546/job/91592311808

Summary:

• mkdocs gh-deploy/mkdocs build fails on docs/tables/mat_view.md with AttributeError: 'NoneType' object has no attribute 'replace' -> Link to failing workflow
• Root cause is upstream: Pygments 2.20.0's HtmlFormatter.__init__ does html.escape(options.get('filename', '')), but pymdown-extensions always explicitly passes filename=title if not inline else "". For any fenced code block without an explicit title= option (i.e. virtually all of them), title is None, so pygments receives filename=None and crashes on .replace(). - Filed and fixed upstream (pygments/pygments#3078) but not yet in a released version
  • 2.20.0 is still latest on PyPI.

Fix

• tighten the pin to Pygments>=2.19.1,<2.20 (matches pymdown-extensions' own floor) until a 2.20.1 release ships the fix, then remove the ceiling.