lang/vala: update to 0.56.3

Changelog:

• Various improvements and bug fixes:
  • vala: Don't unconditionally expect ObjectType of Class [#1341]
  • vala: Make try-statement parsing more resilient [#1304]
  • vala: Avoid problems with '\' in #line directives on Windows [#1353]
  • gidlparser: Set source reference of parameters
• Bindings:
  • atspi-2: Fix a few binding errors
  • glib-2.0: Use g_abort for GLib.Process.abort() beginning with 2.50 [#1350]
  • gtk+-3.0: Correctly unhide BindingSet.by_class to avoid Version attribute