Fix setting property namespace for unsupported AGP

Author: nohli

android/build.gradle

@@ -27,7 +27,12 @@ apply plugin: 'kotlin-android'
 android {
     compileSdkVersion 31
 
-    namespace = 'dev.fluttercommunity.android_id'
+    // Only set namespace on compatible versions (Android Gradle plugin >= 7.0.0)
+    // The if-check checks for a property that has been removed since AGP 7.0.0
+    // https://developer.android.com/build/releases/past-releases/agp-7-0-0-release-notes#build-cache-removed
+    if (!project.hasProperty("android.buildCacheDir")) {
+        namespace = 'dev.fluttercommunity.android_id'
+    }
 
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8