Fix lint warning that breaks gradle build

Calling AudioManager.isOffloadedPlaybackSupported is available since API 29 only.

PiperOrigin-RevId: 398229498

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -1634,6 +1634,7 @@ public final class DefaultAudioSink implements AudioSink {
     }
     }
   }
   }
 
 
+  @RequiresApi(29)
   @C.AudioManagerOffloadMode
   @C.AudioManagerOffloadMode
   private int getOffloadedPlaybackSupport(
   private int getOffloadedPlaybackSupport(
       AudioFormat audioFormat, android.media.AudioAttributes audioAttributes) {
       AudioFormat audioFormat, android.media.AudioAttributes audioAttributes) {