sagemathgh-37134: minor details in quadratic forms

    
slight modernisation of the modified file

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
    
URL: sagemath#37134
Reported by: Frédéric Chapoton
Reviewer(s): Kwankyu Lee