Issue #3397890 by mstrelan, dww: Fix strict type errors in unit tests

core/modules/ban/tests/src/Unit/BanMiddlewareTest.php

.../migrate_drupal/tests/src/Unit/MigrationStateUnitTest.php

core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php

core/modules/update/tests/src/Unit/UpdateFetcherTest.php

...ests/Drupal/Tests/Component/Datetime/DateTimePlusTest.php

...ependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php

core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php

...ests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php

core/tests/Drupal/Tests/Core/Form/FormStateTest.php

core/tests/Drupal/Tests/Core/Password/PhpPasswordTest.php

core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php

.../tests/Drupal/Tests/Core/Render/RendererRecursionTest.php

core/tests/Drupal/Tests/Core/Render/RendererTest.php

core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php

core/tests/Drupal/Tests/Core/Utility/LinkGeneratorTest.php