Restore specs on the CI

[kennyadsl]

Summary

CI is currently not executing any spec, because Solidus is not installed (due to the Rails 7.1 incompatibility) and its specs are not copied over the sandbox application.

Tests were green because there were no tests, so no failures.

Checklist

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• [ ] I have written a thorough PR description.
• [ ] I have kept my commits small and atomic.
• [ ] I have used clear, explanatory commit messages.

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• 📖 I have updated the README to account for my changes.
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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (be2126d) 0.00% compared to head (e3d9dbc) 97.33%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #360 +/- ## ========================================= + Coverage 0 97.33% +97.33% ========================================= Files 0 188 +188 Lines 0 4532 +4532 ========================================= + Hits 0 4411 +4411 - Misses 0 121 +121 ```

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