Update nullness issue in SilkCastApiImpl.java,SessionCallback.java

Null check warning was reported by //java/com/google/android/apps/gsa/staticplugins/silk/silkcast:silkcast_nullness_checker

//third_party/java_src/android_libs/exoplayer/v2/extensions/media2/src/main:library_nullness_test

PiperOrigin-RevId: 343939763

extensions/media2/src/main/java/com/google/android/exoplayer2/ext/media2/SessionCallback.java

@@ -349,6 +349,7 @@ import java.util.concurrent.TimeoutException;
     }
 
     @Override
+    @SuppressWarnings("nullness:override.param.invalid")
     public void onCurrentMediaItemChanged(SessionPlayer player, MediaItem item) {
       currentMediaItemBuffered = isBufferedState(player.getBufferingState());
       updateAllowedCommands();