devel/glib20: update to 2.80.4

Changelog: https://gitlab.gnome.org/GNOME/glib/-/blob/2.80.4/NEWS

While here, belated GTKDOC -> DOC, as gi-docgen replaced gtk-doc
in 2.80.0. Only a subset of the API reference and tools documentation
are generated when introspection is disabled.

(cherry picked from commit 3b2b89d43422ed98433c70d4c9af1af0240953e5)