[tests] fix deprecation numpy warning (#4439)

tests/python_package_test/test_basic.py

@@ -170,7 +170,7 @@ def test_sequence(tmpdir, sample_count, batch_size, include_0_and_nan, num_seq):
     # Test for validation set.
     # Select some random rows as valid data.
     rng = np.random.default_rng()  # Pass integer to set seed when needed.
-    valid_idx = (rng.random(10) * nrow).astype(np.int)
+    valid_idx = (rng.random(10) * nrow).astype(np.int32)
     valid_data = data[valid_idx, :]
     valid_X = valid_data[:, :-1]
     valid_Y = valid_data[:, -1]