Update report testset file extension

[PierreMesure]

Description

Fixes #2057

Related Issue

Fixes #2057

Type of Change

• 📚 Examples / docs / tutorials / dependencies update
• 🔧 Bug fix (non-breaking change which fixes an issue)
• 🥂 Improvement (non-breaking change which improves an existing feature)
• 🚀 New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 🔐 Security fix

Checklist

• I've read the CODE_OF_CONDUCT.md document.
• I've read the CONTRIBUTING.md guide.
• I've written tests for all new methods and classes that I created.
• I've written the docstring in Google format for all the methods and classes that I used.
• I've updated the pdm.lock running pdm update-lock (only applicable when pyproject.toml has been
  modified)

[henchaves]

well spotted! thanks a lot @PierreMesure