Fix logic to allow all iterables (not only lists)

[LilianBoulard]

This fixes an issue in the notebook, as seen here:

Traceback (most recent call last):
  File "/home/circleci/project/examples/01_dirty_categories.py", line 321, in <module>
    feature_names = sup_vec.get_feature_names()
  File "/home/circleci/project/dirty_cat/super_vectorizer.py", line 488, in get_feature_names
    return self.get_feature_names_out()
  File "/home/circleci/project/dirty_cat/super_vectorizer.py", line 456, in get_feature_names_out
    ct_feature_names = super().get_feature_names_out()
  File "/home/circleci/miniconda/envs/testenv/lib/python3.8/site-packages/sklearn/compose/_column_transformer.py", line 479, in get_feature_names_out
    feature_names_out = self._get_feature_name_out_for_transformer(
  File "/home/circleci/miniconda/envs/testenv/lib/python3.8/site-packages/sklearn/compose/_column_transformer.py", line 451, in _get_feature_name_out_for_transformer
    return trans.get_feature_names_out(names)
  File "/home/circleci/project/dirty_cat/gap_encoder.py", line 749, in get_feature_names_out
    elif col_names == 'auto':
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

it's a simple fix really, just reorganizing the logic so that not only lists are supported, but iterables in general.