Fix test failure due to recent change to ShadowAudioTrack

<unknown commit> used a new API provided in API29+, changing this test's config to
use the newer SDK version.

TAP:https://test.corp.google.com/ui#d=targetZoomout&flags=CAMQAlhg&t=//third_party/java_src/android_libs/exoplayer/v2/library/core/src/test:test_com/google/android/exoplayer2/audio/MediaCodecAudioRendererTest
PiperOrigin-RevId: 328344926

library/core/src/test/java/com/google/android/exoplayer2/audio/MediaCodecAudioRendererTest.java

@@ -49,8 +49,10 @@ import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnit;
 import org.mockito.junit.MockitoRule;
+import org.robolectric.annotation.Config;
 
 /** Unit tests for {@link MediaCodecAudioRenderer} */
+@Config(sdk = 29)
 @RunWith(AndroidJUnit4.class)
 public class MediaCodecAudioRendererTest {
   @Rule public final MockitoRule mockito = MockitoJUnit.rule();