Fix test.

Author: trivialfis

src/learner.cc

@@ -1160,13 +1160,13 @@ class LearnerImpl : public LearnerIO {
     }
 
     this->ValidateDMatrix(train.get(), true);
-
-    CHECK_GE(this->learner_model_param_.OutputLength(), in_gpair->NumSplitTargets())
-        << "The number of columns in gradient should be equal to or lesser than the number of "
-           "targets/classes in the model.";
     if (in_gpair->HasValueGrad()) {
       CHECK_EQ(this->learner_model_param_.OutputLength(), in_gpair->NumTargets())
           << "Value gradient should have the same number of targets as the overall model.";
+    } else {
+      CHECK_EQ(this->learner_model_param_.OutputLength(), in_gpair->NumSplitTargets())
+          << "The number of columns in gradient should be equal to the number of "
+             "targets/classes in the model.";
     }
     auto predt = prediction_container_.Cache(train, ctx_.Device());
     this->gbm_->DoBoost(train.get(), in_gpair, predt.get(), obj_.get());