Update regression test description for x_column config

Author: mo374z

tests/tasks/test_reward_tasks.py

@@ -57,7 +57,7 @@ def reward_fn(prediction: str, reward: float) -> float:
 
 
 def test_reward_task_x_column_from_config(simple_reward_function):
-    """Regression for issue #67."""
+    """Ensure setting an arbitrary x_column name via the config works."""
     df = pd.DataFrame({"my_input": ["a", "b", "c"]})
     config = ExperimentConfig(x_column="my_input")
     task = RewardTask(df=df, reward_function=simple_reward_function, config=config)