fix(showcase): use NoCredentialsProvider in ITOtelErrorType tests to avoid ADC issues in CI

Author: diegomarquezp

sdk-platform-java/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/it/ITOtelErrorType.java

@@ -149,6 +149,7 @@ public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
 
     EchoSettings grpcEchoSettings =
         EchoSettings.newBuilder()
+            .setCredentialsProvider(NoCredentialsProvider.create())
             .setTransportChannelProvider(
                 EchoSettings.defaultGrpcTransportProviderBuilder()
                     .setChannelConfigurator(ManagedChannelBuilder::usePlaintext)