vala: update to 0.40.4.

Vala 0.40.4
===========
* Various improvements and bug fixes:
  - girparser: Add support for NoAccessorMethod metadata

* Bindings:
  - glib-2.0: Mark str parameter of Variant.take_string() as owned
  - gstreamer: Update from 1.15+ git master
  - gtk+-*.0: Set NoAccessorMethod on Gtk.Radio*.group properties
    (Regression in gtk+-3.0)
  - gtk+-4.0: Update to 3.93.0+fc6018f1
  - json-glib-1.0: Mark return-type of gvariant_deserialize*() as nullable
  - webkit2gtk-4.0: Update to 2.20.1

(wiz)