Suppress MissingClassConstType if the class is final

[ThomasLandauer]

MissingClassConstType was added in #10828 by @jack-worman

The RFC kinda mentions that typed constants are only useful with regard to child classes - see https://wiki.php.net/rfc/typed_class_constants

By default, child classes can override class constants of their parents, so sometimes it is not easy to assume what the value and the type of a class constant really is, unless either their defining class or the constant itself is final

So when a class is final (=best practice for most classes today), there's no need to to type something like const foo = 5;, since it's obvious that it's an int.

So I'm suggesting to restrict MissingClassConstType to cases where neither the class nor the const itself are final.

[psalm-github-bot]

Hey @ThomasLandauer, can you reproduce the issue on https://psalm.dev? These will be used as phpunit tests when implementing the feature or fixing this bug.