Update to Java 21 + hardcode NDK to avoid warnings

.github/workflows/release.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: 'temurin' # See 'Supported distributions' for available options
-          java-version: '17'
+          java-version: '21'
 
       - name: Flutter Doctor
         id: flutter_doctor

android/app/build.gradle.kts

@@ -29,7 +29,7 @@ if (keystorePropertiesFile.exists()) {
 android {
     namespace = "dev.imranr.obtainium"
     compileSdk = flutter.compileSdkVersion
-    ndkVersion = flutter.ndkVersion
+    ndkVersion = "27.0.12077973" // 'flutter.ndkVersion' produces warnings (TODO can/should we switch back?)
 
     compileOptions {
         isCoreLibraryDesugaringEnabled = true

docker/Dockerfile

@@ -51,7 +51,7 @@ RUN \
     mv ${ANDROID_SDK_ROOT}/cmdline-tools/cmdline-tools ${ANDROID_SDK_ROOT}/cmdline-tools/latest && \
     rm -v /tmp/tools.zip && \
     mkdir -p /root/.android/ && touch /root/.android/repositories.cfg &&\
-    apt-get install -y --no-install-recommends openjdk-17-jdk openjdk-17-jre &&\
+    apt-get install -y --no-install-recommends openjdk-21-jdk openjdk-21-jre &&\
     yes | sdkmanager --licenses &&\
     sdkmanager --update