package/webkitgtk: bump to version 2.24.3

Version 2.24.3 is a minor update which contains many bugfixes.
>From the announcement:

  - Fix previous/next gestures in RTL mode.
  - Fix rendering artifacts in popular sites (YouTube, GitHub, etc.)
  - Fix media playback annoyances (volume randomly changing, HLS streams
    starting too slowly, some audio streams would not play, etc.)
  - Fix build with audio and video disabled.

  https://webkitgtk.org/2019/07/02/webkitgtk2.24.3-released.html



Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>