Fix whitespace in `GetIsManageStockForProduct.php`

[convenient]

Description (*)

This is purely fixing some whitespace in the code. I can't imagine much testing is needed here 🤞 but let me know if / what you want.

Contribution checklist (*)

• [ ] Pull request has a meaningful description of its purpose
• [ ] All commits are accompanied by meaningful commit messages
• [ ] All new or changed code is covered with unit/integration tests (if applicable)
• [ ] All automated tests passed successfully (all builds are green)