Fix Ruby test that failed to read initial metadata

src/ruby/spec/client_server_spec.rb

@@ -198,6 +198,7 @@ shared_examples 'basic GRPC message delivery is OK' do
     # confirm the client can receive the server response and status.
     client_ops = {
       CallOps::SEND_CLOSE_FROM_CLIENT => nil,
+      CallOps::RECV_INITIAL_METADATA => nil,
       CallOps::RECV_MESSAGE => nil,
       CallOps::RECV_STATUS_ON_CLIENT => nil
     }