Update to 0.56.19

Various improvements and bug fixes:

• codegen: Minor refactoring of TypeRegisterFunction and its subclasses
• codegen: Use G_TYPE_FLAG_NONE when targetting glib >= 2.74
• codegen: Use g_once_init_{enter,leave}_pointer when targetting glib >= 2.80
• codegen: Propagate default_value_on_error from parent struct
• codegen: Return default_value_on_error on precondition failures
• gdbus: Avoid unused variables in method call and properties getter/setter
• gdbus: Allow GLib.VariantDict for a{sv}
• gdbus: Do not provide unintended read/write access to properties
• parser: Fix statement error recovery [#1590]
• vala: Use reference-transfer as needed when transforming conditional-expression [#1648]
• girwriter: Don't use instance-parameter inside function elements [#1606]
• girwriter: Add the doc:format argument in the .gir file
• libvaladoc: Do not error-out on doc:format
• libvaladoc: Add compat layer for gvRenderData to cope with API break [#1621]

Bindings:

• glib-2.0: allow FileUtils.open_tmp's first argument to be null
• posix: add UTIME_{NOW,OMIT} constants for utimensat
• gsl: Deprecate gsl_linalg_cholesky_decomp in favour of gsl_linalg_cholesky_decomp1 [#1602]
• libxml-2.0: Add more fields to ParserCtxt
• gobject-2.0: Set default_value{,_on_error} for GType
• glib-2.0: Fix *.add_once () callbacks [#1556]
• gobject-2.0: Fix return type
• gobject-2.0: Add Type.to_string ()
• gstreamer-1.0: Fix ownership of Caps.full*() parameters [#1628]
• glib-2.0: fix a typo in a parameter name
• gtk4: Update to 4.21.6+83716767
• gtk4: Make all Gsk.RenderNode and Gsk.Renderer shadow their parent type
• gtk4: Fix CursorGetTextureCallback declaration