Try changing android min-sdk to 21 because :grpc-android-interop-test…

…ing:mergeDexDebug task is failing with

> Could not resolve all files for configuration ':grpc-android-interop-testing:debugRuntimeClasspath'.
   > Failed to transform annotation-jvm-1.9.1.jar (androidx.annotation:annotation-jvm:1.9.1) to match attributes {artifactType=android-dex, asm-transformed-variant=NONE, dexing-enable-desugaring=true, dexing-enable-jacoco-instrumentation=false, dexing-is-debuggable=true, dexing-min-sdk=20, org.gradle.category=library, org.gradle.jvm.environment=standard-jvm, org.gradle.libraryelements=jar, org.gradle.status=release, org.gradle.usage=java-runtime, org.jetbrains.kotlin.platform.type=jvm}.
      > Execution failed for DexingWithClasspathTransform: /root/.gradle/caches/modules-2/files-2.1/androidx.annotation/annotation-jvm/1.9.1/b17951747e38bf3986a24431b9ba0d039958aa5f/annotation-jvm-1.9.1.jar.
         > Error while dexing.
   > Failed to transform kotlin-stdlib-1.9.24.jar (org.jetbrains.kotlin:kotlin-stdlib:1.9.24) to match attributes {artifactType=android-dex, asm-transformed-variant=NONE, dexing-enable-desugaring=true, dexing-enable-jacoco-instrumentation=false, dexing-is-debuggable=true, dexing-min-sdk=20, org.gradle.category=library, org.gradle.libraryelements=jar, org.gradle.status=release, org.gradle.usage=java-runtime}.
      > Execution failed for DexingWithClasspathTransform: /root/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.9.24/9928532f12c66ad816a625b3f9984f8368ca6d2b/kotlin-stdlib-1.9.24.jar.
         > Error while dexing.

android-interop-testing/src/main/AndroidManifest.xml

@@ -7,6 +7,7 @@
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
     <uses-sdk tools:overrideLibrary="io.grpc.android"/>
+    <uses-sdk android:minSdkVersion="21"/>
 
     <application
         android:allowBackup="true"