Fix PHPStan level 5 errors

Problem/Motivation

PHPStan reports various level 5 errors.

Proposed resolution

Address reported level 5 errors.

Reported errors

• Parameter #1 $code of method Behat\Mink\WebAssert::statusCodeEquals() expects int, string given. In devel_generate/tests/src/Functional/DevelGenerateBrowserTest.php:73
• Parameter #1 $code of method Behat\Mink\WebAssert::statusCodeEquals() expects int, string given. In devel_generate/tests/src/Functional/DevelGenerateBrowserTest.php:105
• Parameter #4 $field_label of method Drupal\Tests\devel_generate\Functional\DevelGenerateBrowserTestBase::createEntityReferenceField() expects string, null given. In devel_generate/tests/src/Traits/DevelGenerateSetupTrait.php (in context of class Drupal\Tests\devel_generate\Functional\DevelGenerateBrowserTestBase)
• Parameter #4 $field_label of method Drupal\Tests\devel_generate\Functional\DevelGenerateCommandsTest::createEntityReferenceField() expects string, null given. In devel_generate/tests/src/Traits/DevelGenerateSetupTrait.php (in context of class Drupal\Tests\devel_generate\Functional\DevelGenerateCommandsTest)
• Parameter #1 $plugin_id of method Drupal\Component\Plugin\FallbackPluginManagerInterface::getFallbackPluginId() expects string, null given. In src/Form/SettingsForm.php
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:31
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:43
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:65
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:81
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:104
• Parameter #2 $option of method Drupal\Tests\WebAssert::optionExists() expects string, int given. In tests/src/Functional/DevelErrorHandlerTest.php:105
• Parameter #2 $name of method Drupal\KernelTests\Core\Entity\EntityKernelTestBase::createUser() expects string|null, array<int, string> given. In tests/src/Kernel/DevelEntityToArrayTest.php:61
• Parameter #4 $langcode of method Drupal\Core\Mail\MailManagerInterface::mail() expects string, Drupal\Core\Language\LanguageInterface given. In tests/src/Kernel/DevelMailLogTest.php:154
• Parameter #4 $langcode of method Drupal\Core\Mail\MailManagerInterface::mail() expects string, Drupal\Core\Language\LanguageInterface given. In tests/src/Kernel/DevelMailLogTest.php:166
• Parameter #4 $langcode of method Drupal\Core\Mail\MailManagerInterface::mail() expects string, Drupal\Core\Language\LanguageInterface given. In tests/src/Kernel/DevelMailLogTest.php:179