gh-36180: more fixes in quadratic forms
This is fixing a few code and doc details in two files inside quadratic
forms.
### :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/36180
Reported by: Frédéric Chapoton
Reviewer(s): Frédéric Chapoton, Matthias Köppe, Travis Scrimshaw
