Reintroduce PHPStan and fix phpstan errors

Last PHPStan error suggests removing the ban migrate source plugin, since that module is currently deprecated and will be removed in Drupal 12. Unsure if we should really do that. I'd prefer not to.

Sorry, this has not fixed phpstan, it's just lowered the level from 8 to 0. Would be better to add the appropriate return types. I hadn't added them initially because it would mean a BC break, so I've added to the baseline instead.

@mstrelan that is true, since removing it we use https://git.drupalcode.org/project/gitlab_templates/-/blob/main/assets/p... instead.

But this is usually the standard for most contrib modules, why should we use a dedicated phpstan.neon for this module specifically?

I don't see it as the standard, more as the lack of standard. In fact, Drupal core uses level 1, and ban was previously subject to that. By reverting to level 0 we're going even lower than core.

The documentation for PHPStan in Gitlab Templates (for contrib) is at https://project.pages.drupalcode.org/gitlab_templates/jobs/phpstan/ and suggests that the default configuration is a fallback for when you haven't provided your own:

Configuration discovery leverages PHPStan's defaults: it will use phpstan.neon when present, fall back to phpstan.neon.dist, and finally phpstan.dist.neon. If none of these exist in the project root, a default configuration is used.

Furthermore, I don't know why you wouldn't want to have better automated checks in place, particularly when there are so few violations to start with.

LGTM, thanks!

perfect, thanks!