Fix expected error code in test

Author: guerler

lib/galaxy_test/api/test_histories.py

@@ -1334,4 +1334,4 @@ def test_other_users_history_is_forbidden(self):
 
     def test_nonexistent_history_is_rejected(self):
         response = self.dataset_populator.get_history_graph_raw("0000000000000000")
-        self._assert_status_code_is(response, 404)
+        self._assert_status_code_is(response, 400)