Test on s390x. (#7038)

* Fix && remove unused parameter.

tests/python/test_basic.py

@@ -232,6 +232,7 @@ class TestBasic:
         assert isinstance(cv, dict)
         assert len(cv) == (4)
 
+    @pytest.mark.skipif(**tm.skip_s390x())
     def test_cv_explicit_fold_indices_labels(self):
         params = {'max_depth': 2, 'eta': 1, 'verbosity': 0, 'objective':
                   'reg:squarederror'}

tests/python/testing.py

@@ -11,6 +11,7 @@ import pytest
 import tempfile
 import xgboost as xgb
 import numpy as np
+import platform
 
 hypothesis = pytest.importorskip('hypothesis')
 sklearn = pytest.importorskip('sklearn')
@@ -136,6 +137,12 @@ def no_multiple(*args):
     return {'condition': condition, 'reason': reason}
 
 
+def skip_s390x():
+    condition = platform.machine() == "s390x"
+    reason = "Known to fail on s390x"
+    return {"condition": condition, "reason": reason}
+
+
 # Contains a dataset in numpy format as well as the relevant objective and metric
 class TestDataset:
     def __init__(self, name, get_dataset, objective, metric