gh-36703: make modform rings for triangle groups use Algebras
    
This is using the category framework in a few more rings, namely modular
forms for triangle groups.

### 📝 Checklist

- [ ] The title is concise, informative, and self-explanatory.
- [ ] The description explains in detail what this PR is about.
    
URL: #36703
Reported by: Frédéric Chapoton
Reviewer(s): Kwankyu Lee

Author: Release Manager