Log Message:
vala: update to 0.56.7.

Vala 0.56.7
===========
 * Various improvements and bug fixes:
  - codegen:
    + Fix usage of lambda-expression from delegate initializer [#1428]
  - vala:
    + Check type-argument count of interface prerequisites
    + Improve Symbol.to_string() to include TypeParameters
    + Improve error message for wrong number of type-arguments
    + Improve check of type_reference in ObjectCreationExpression
    + Allow inheritance from sealed class in bindings [#1036]
  - Fix a couple of type-argument issues in vala itself
  - g-i: Fix compiling with mingw clang

 * Bindings:
  - gio-2.0,glib-2.0,gtk+-3.0,gtk4: Fix a few binding issues
  - glib-2.0: g_chdir is declared in <glib/gstdio.h>