[Codecept5] Return type fixes

[yesdevnull]

This adds return types for several methods that implement core Codeception 5 interfaces which have return types.

[TavoNiievez]

Same story here, your changes were already in the codecept5 branch, now that I changed the target branch there are no changes left to apply.

Anyway I'll redo my previous commit to include you as a co-author.
Please read my other comment.