ci: use flutter_package workflow

[alestiago]

Description

The CI is broken due to dart pub get reporting:

Because example depends on flutter_test from sdk which doesn't exist (the Flutter SDK is not available), version solving failed.

This is because the example depends on flutter and dart pub get attempts to get on /example.

Changes:

• Updates workflow to use flutter_package over dart_package.
• Sets flutter_package workflow to use Flutter 3.13.0

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
• 📝 Documentation
• 🗑️ Chore