input: Write a python function to evaluate a linear regression model using r2_score.
  assert evaluate_model([1, 2, 3], [1, 2, 3]) == 1.0
  assert evaluate_model([1, 2, 3], [2, 3, 4]) == 0.5
  assert evaluate_model([1, 2, 3], [3, 2, 1]) == -3.0
output: from sklearn.metrics import r2_score
  
  def evaluate_model(y_true, y_pred):
      return r2_score(y_true, y_pred)