chore(curriculum): remove `__locals` from Luhn algorithm

[ilenia-magoni]

Checklist:

• [x] I have read and followed the contribution guidelines.
• [x] I have read and followed the how to open a pull request guide.
• [x] My pull request targets the main branch of freeCodeCamp.
• [x] I have tested these changes either locally on my machine, or GitPod.

Found this comment, working on it

https://github.com/ilenia-magoni/freeCodeCamp/blob/df22f5834f4680070bf25bb6b74ad5e7d2524df1/tools/client-plugins/browser-scripts/python-test-evaluator.ts#L175-L176