external_entities_form_field_storage_config_edit_form_alter does not work correctly

Problem/Motivation

It looks for ::validateCardinality but if I inspect the callback I see [$this, 'validateCardinality'] (defined in FieldStorageConfigEditForm::getCardinalityForm()).

Steps to reproduce

Save an external entity field config.
FieldStorageConfigEditForm::validateCardinality() is called (and triggers errors in our external storage class because we don't handle deltas).

Proposed resolution

It should look for an array item containing validateCardinality.