Added GH ref

Author: MomIsBestFriend

pandas/tests/reductions/test_reductions.py

@@ -826,6 +826,7 @@ def test_all_any_params(self):
         s1 = Series([np.nan, True])
         s2 = Series([np.nan, False])
 
+        # GH #12863
         assert s1.all(skipna=True)
         assert s1.any(skipna=True)