Fix test.

Author: trivialfis

tests/python/test_ranking.py

@@ -76,7 +76,7 @@ def test_ranking_with_weighted_data():
         assert all(p <= q for p, q in zip(is_sorted, is_sorted[1:]))
 
 
-def test_error_msg(self) -> None:
+def test_error_msg() -> None:
     X, y, qid, w = tm.make_ltr(10, 2, 2, 2)
     ranker = xgboost.XGBRanker()
     with pytest.raises(ValueError, match=r"equal to the number of query groups"):