workmanager v0.10.6 — AGP 9 fix

workmanager_android v0.10.5 — AGP 9 + android.builtInKotlin=false fix (#722)

• The plugin failed to evaluate on AGP 9 with Flutter's default android.builtInKotlin=false (Could not find method kotlin()); 0.9.x failed even harder (plugin class never compiled).
• Fix: apply kotlin-android whenever built-in Kotlin is not active — AGP < 9, or android.builtInKotlin != true — matching AGP 9's own defaults (built-in Kotlin on by default). Same pattern flutter_timezone 5.1.0 ships. Thanks @EdwynZN (#721).
• Verified on AGP 9.0.1 both flag modes + AGP 8.11 regression (50 unit tests).

workmanager v0.10.6

• Dependency bump: workmanager_android ^0.10.5.