fix types

Author: nimf

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/gaxx/grpc/fallback/GcpFallbackChannel.java

@@ -382,7 +382,7 @@ public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedE
 
   @Override
   public List<? extends BigtableChannelObserver> getChannelInfos() {
-    List<? extends BigtableChannelObserver> channelInfos = new ArrayList<>();
+    List<BigtableChannelObserver> channelInfos = new ArrayList<>();
     if (primaryDelegateChannel != null
         && primaryDelegateChannel instanceof BigtableChannelPoolObserver) {
       channelInfos.addAll(((BigtableChannelPoolObserver) primaryDelegateChannel).getChannelInfos());