Update test_crosstab.py

Author: simonjayhawkins

pandas/tests/reshape/test_crosstab.py

@@ -746,6 +746,7 @@ def test_margin_normalize_multiple_columns(self):
 
 
 def test_categoricals():
+    # https://github.com/pandas-dev/pandas/issues/37465
     g = np.random.RandomState(25982704)
     a = Series(g.randint(0, 3, size=100)).astype("category")
     b = Series(g.randint(0, 2, size=100)).astype("category")