[css-view-transitions-1] The update callback queue has multiple issues.

[Psychpsyo]

Hello, I'm currently implementing this in the Ladybird browser and:

1. Flush the update callback queue takes a document, but is never called with a document.
2. Schedule the update callback refers to "transition’s relevant settings object’s update callback queue".
   The other specs are a bit hard to follow here, but it seems to me like an environment settings object is a different thing from a document, which is where the update callback queue lives.