Fix id for EntityReferenceSelection

Created a new MR.

AstonVictor → closed merge request !13

AstonVictor → reopened merge request !13

for reproducing the error:

$selection_manager = \Drupal::service('plugin.manager.entity_reference_selection');
$handler = $selection_manager->getPluginId('user_role', 'role_change');

I have successfully replicated the issue we discussed earlier. For reference, I have attached a screenshot highlighting the specific error.
MR !13 fixing this issue.