fix(bigtable): make ignoreError volatile (#13218)

Author: mutianf

java-bigtable/google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/channels/FallbackChannelPool.java

@@ -135,7 +135,7 @@ public SessionStream newStream(
     final SessionStream stream = current.newStream(desc, callOptions);
 
     return new ForwardingSessionStream(stream) {
-      private boolean ignoreError;
+      private volatile boolean ignoreError;
 
       @Override
       public void start(Listener responseListener, Metadata headers) {