Updated: Comment #0
\Drupal\search\Form\SearchSettingsForm contains a "use" statement for \Drupal\Core\Extension\ModuleHandler but that class is not used. Because it is (incorrectly) type-hinted as a member variable PhpStorm does not report it as unused.
Fix the type-hint and remove the "use" statement.
Review & commit the patch.
- This was introduced in recently.