fix(android): Support AGP 9+

Guards apply plugin: 'kotlin-android' because AGP 9 pre-registers the
kotlin extension itself (built-in Kotlin support), so a second registration
throws Cannot add extension with name 'kotlin'.

On AGP 8 the guard is false → unchanged. On AGP 9 the apply is skipped
AGP supplies Kotlin compilation via its bundled KGP 2.2.10.

Source: https://developer.android.com/build/migrate-to-built-in-kotlin

Fixes #815

Author: peitschie

.github/workflows/main.yml

@@ -38,6 +38,15 @@ jobs:
 
   verify-android:
     runs-on: ubuntu-24.04
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - agp: '8.13.0'
+            gradle: '8.14.3'
+          - agp: '9.1.1'
+            gradle: '9.3.1'
+    name: verify-android (AGP ${{ matrix.agp }} / Gradle ${{ matrix.gradle }})
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v4
@@ -48,7 +57,12 @@ jobs:
           java-version: '21'
           distribution: 'zulu'
       - run: npm ci
-      - run: npm run verify:android
+      - name: Update Gradle wrapper to ${{ matrix.gradle }}
+        working-directory: android
+        run: ./gradlew wrapper --gradle-version=${{ matrix.gradle }} --distribution-type=all
+      - name: Build & test with AGP ${{ matrix.agp }}
+        working-directory: android
+        run: ./gradlew clean build test -PagpVersion=${{ matrix.agp }}
 
   verify-ios:
     runs-on: macos-15

android/build.gradle

@@ -16,13 +16,15 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:8.13.0'
+        classpath "com.android.tools.build:gradle:${project.findProperty('agpVersion') ?: '8.13.0'}"
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
 apply plugin: 'com.android.library'
-apply plugin: 'kotlin-android'
+if (project.extensions.findByName('kotlin') == null) {
+    apply plugin: 'kotlin-android'
+}
 
 android {
     namespace = "com.capacitorjs.community.plugins.bluetoothle"