[fix] [test] Fix an error in test

The previous version provided non-sparse data at the training and sparse
data at the test time, which is invalid.
That is why I fixed this error.

Author: nabenabe0928

test/test_data/test_validation.py

@@ -103,7 +103,7 @@ def test_sparse_data_validation_for_regression():
 
     validator.fit(X_train=X_sp, y_train=y)
 
-    X_t, y_t = validator.transform(X, y)
+    X_t, y_t = validator.transform(X_sp, y)
     assert np.shape(X) == np.shape(X_t)
 
     # make sure everything was encoded to number