eeejay
docs: fix missing annotation
GObject-Introspection now supports annotating the async/finish functions, although the language bindings must support this to allow automatic await support.
In the most current release the GIR compiler, and probably gi-docgen, will emit warning if it can't match find a matching pair of some_async()/some_finish(), as is the case with spiel_speaker_new() and spiel_speaker_new_finish().
The patch adds that annotation, but should be verified to pass the CI on a GNOME 46 distribution before merge or it may result in an error on older versions.
I'm marking this as a draft, since I don't have a container handy just now to check what happens on e.g. fedora:39. It may cause gi-docgen or g-ir-compiler to choke on an unrecognized annotation and it'll be a month or so before distros start to roll out GNOME 46.