Log Message:
vala: update to 0.48.6.

Vala 0.48.6
===========
 * Regression and bug fixes:
  - codegen:
    + Correctly handle cast-expression of real struct to nullable struct [#991]
    + Use loop index instead of get_ccode_pos() for ellipsis parameter [#995]
  - vala:
    + Allow node_ref being null in SemanticAnalyzer.get_instance_base_type()
    + SemanticAnalyzer.get_instance_base_type() is not allowed to return null
    + params-array parameter is not allowed in abstract/virtual method [#985]
    + Use stable hash for methods in HashMap of implicit_implementations [#990]
      and Use "str_equal" as equal_func for ArrayList<string> \ 
instances
    + Set value_type of undefined member-access to avoid further criticals
    + Transform cast from floating-type to boxed-type [#991]
    + Transform cast from integer-type to boxed-type [#992]
    + Explicit "new" method may be incompatible with a posssible base \ 
method
  - valadoc: Add implicit "Posix" using-directive for POSIX profile
  - girparser: Add support for boolean "new" argument for methods

 * Bindings:
  - gtk4: Update to 3.98.3+028942c8