Log Message:
vala: updated to 0.56.8

Vala 0.56.8
===========
 * Various improvements and bug fixes:
  - codegen: Include "glib-object.h" when using GType/GBoxedCopyFunc
  - valadoc: Backing method of lambda-expression isn't included in valadoc AST
  - valadoc/tests: Add girwriter test
  - build: Improve usage of AC_PATH_PROG() for valacs
  - build: valadoc requires valac 0.18.1

 * Bindings:
  - gio-2.0: Add new symbols from 2.76
  - glib-2.0: Add new symbols from 2.76
  - glib-2.0: Fix binding of g_variant_type_n_items()
  - gtk4: Don't skip AlertDialog ctor