docs(flutter_infinite_list): update tutorial

[LukasMirbt]

Status

READY

Breaking Changes

NO

Description

• Updates tutorial to reflect the latest state of the code

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [x] 📝 Documentation
• [ ] 🗑️ Chore