update dataframe test_describe

`null_count` was fixed upstream.

Ref apache/datafusion#10260

Author: Michael-J-Ward

datafusion/tests/test_dataframe.py

@@ -730,9 +730,9 @@ def test_describe(df):
             "max",
             "median",
         ],
-        "a": [3.0, 3.0, 2.0, 1.0, 1.0, 3.0, 2.0],
-        "b": [3.0, 3.0, 5.0, 1.0, 4.0, 6.0, 5.0],
-        "c": [3.0, 3.0, 7.0, 1.7320508075688772, 5.0, 8.0, 8.0],
+        "a": [3.0, 0.0, 2.0, 1.0, 1.0, 3.0, 2.0],
+        "b": [3.0, 0.0, 5.0, 1.0, 4.0, 6.0, 5.0],
+        "c": [3.0, 0.0, 7.0, 1.7320508075688772, 5.0, 8.0, 8.0],
     }