\Drupal\KernelTests\Core\Render\Element\ActionsTest::getFormId() causes deprecations on PHP 8.1

Problem/Motivation

\Drupal\KernelTests\Core\Render\Element\ActionsTest::getFormId() returns NULL and cause deprecation on PHP 8.1.

Because \Drupal\Core\Form\FormBuilder::prepareForm() calls \Drupal\Component\Utility\Html::getId() with NULL as form ID so mb_strtolower() throws deprecation

 $form['#attributes']['data-drupal-selector'] = Html::getId($form_id);

Steps to reproduce

Run core/tests/Drupal/KernelTests/Core/Render/Element/ActionsTest.php on PHP 8.1

  2x: mb_strtolower(): Passing null to parameter #1 ($string) of type string is deprecated
    2x in ActionsTest::testDropbuttonWithBubbleableMetadata from Drupal\KernelTests\Core\Render\Element

  1x: strrpos(): Passing null to parameter #1 ($haystack) of type string is deprecated
    1x in ActionsTest::testDropbuttonWithBubbleableMetadata from Drupal\KernelTests\Core\Render\Element

Proposed resolution

return string from \Drupal\KernelTests\Core\Render\Element\ActionsTest::getFormId()

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet