gh-40043: Clean mut type
    
mostly pep8 cleanup for spaces around parentheses and brackets

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #40043
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager