Once released, the next version (2.24.32) will appear here: http://ftp.gnome.org/pub/gnome/sources/gtk+/2.24/
Then somebody will need to update the version in MSYS2, you can track `pkgver` here: https://github.com/Alexpux/MINGW-packages/blob/master/mingw-w64-gtk2/PKGBUIL...
Once updated, in a day or two it will be made available as a package in the official [repository](http://repo.msys2.org/mingw/i686/) so it can be updated via `pacman`.