Version 1.64.3

- Closed bugs and merge requests:
  * arg: Don't sink GClosure ref if it's a return value [!426, Philip Chimento]
  * overrides/Gtk: Adjust gtk_container_child_set_property() check [!431,
    Florian Müllner]
  * 1.63.3: test suite is failing [#298, !430, Philip Chimento]
  * Simplify private pointers [!434, Philip Chimento]

- Various backports:
  * Use memory GSettings backend in tests [Philip Chimento]
  * Update debug message from trimLeft/trimRight to trimStart/trimEnd [Philip
    Chimento]
  * Various fixes for potential crash and memory issues [Philip Chimento]