Check if PackId is a digit before casting to int

[solevis]

No description provided.

[sentry]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: backend/app/services/daily_offer.py

Function	Unhandled Issue
get_promotions_from_api	ValueError: invalid literal for int() with base 10: '500starbux' ... Event Count: 739
get_promotions_from_api	ValueError: invalid literal for int() with base 10: '500starbux' app.services.daily_offer in get_pro... Event Count: 5