Rule to check if test classes names end with "Test"

[Boegie]

Feature request

Over in https://www.drupal.org/project/drupal/issues/3268489 catch wrote:

The ending with test feels like something we could add to phpstan - any non-abstract subclass of whatever the root test base class is. I think we should open a follow-up for that. These specific tests aren't going to be renamed again once this goes in and it'll stop regressions that would cause those tests to fail.