text: Title: Missing format string arguments
  Body: This assertion error string is not properly formatted as the 2 format arguments `y_pred.shape` and `y.shape` are missing:
  
  https://github.com/scikit-learn/scikit-learn/blob/551d56c254197c4b6ad63974d749824ed2c7bc58/sklearn/utils/estimator_checks.py#L2139
  
  ```python
  assert y_pred.shape == y.shape, (
      "The shape of the prediction for multioutput data is incorrect."
      " Expected {}, got {}."
  )
  ```
  
  should become
  
  ```python
  assert y_pred.shape == y.shape, (
      "The shape of the prediction for multioutput data is incorrect."
      " Expected {}, got {}.".format(y_pred.shape, y.shape)
  )
  ```