Fix deprecated test code

Problem/Motivation

Some of the code in the automated tests has been deprecated and is not detected by Drupal-Check

  15x: Drupal\Tests\BrowserTestBase::$defaultTheme is required in drupal:9.0.0 when using an install profile that does not set a default theme. See https://www.drupal.org/node/3083055, which includes recommendations on which theme to use.
    1x in ConfigFormTest::testConfiguration from Drupal\Tests\workflow_participants_auto\Functional
    1x in AdminUiNotificationsTest::testNotifications from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testAdminConfiguration from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testUi from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testAuthorUi from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testEditorUi from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testReviewerUi from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testAuthenticatedUsers from Drupal\Tests\workflow_participants\Functional
    1x in AdminUiTest::testCacheTags from Drupal\Tests\workflow_participants\Functional
    1x in EntityAccessTest::testReadAccess from Drupal\Tests\workflow_participants\Functional
    1x in EntityAccessTest::testEditAccess from Drupal\Tests\workflow_participants\Functional
    1x in EntityAccessTest::testLatestVersion from Drupal\Tests\workflow_participants\Functional
    1x in SettingsFormTest::testForm from Drupal\Tests\workflow_participants\Functional\Form
    1x in NonNodeUiTest::testAdminUi from Drupal\Tests\workflow_participants\Functional
    1x in RevisionAccessTest::testRevisionsTab from Drupal\Tests\workflow_participants\Functional

Steps to reproduce

run phpunit