gh-36899: some ruff fixes and error links in the graphs folder
this fixes some ruff warnings and add some ilnks for errors in the doc
in the graphs folder
### :memo: Checklist
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
URL: https://github.com/sagemath/sage/pull/36899
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert
