[PHP 8.4] Fix phpstan job for ContentModerationConfigureEntityTypesForm

Problem/Motivation

Split from manual fixes from #3444232: [8.4] Fix implicitly nullable type declarations for phpstan job (manual ones)

Steps to reproduce

$ docker run --rm -v $(pwd):/var/www/html drupalci/php-8.4-ubuntu-apache:dev php -d error_reporting="E_ALL" -l core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
...
PHP Deprecated:  Drupal\content_moderation\Form\ContentModerationConfigureEntityTypesForm::buildForm(): Implicitly marking parameter $workflow as nullable is deprecated, the explicit nullable type must be used instead in core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php on line 101
PHP Deprecated:  Drupal\content_moderation\Form\ContentModerationConfigureEntityTypesForm::getTitle(): Implicitly marking parameter $workflow as nullable is deprecated, the explicit nullable type must be used instead in core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php on line 221
No syntax errors detected in core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php

Proposed resolution

As both arguments are required according to route definition make $workflow required too

content_moderation.workflow_type_edit_form:
  path: '/admin/config/workflow/workflows/manage/{workflow}/type/{entity_type_id}'

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet