gnu: syncthing-gtk: Wrap with GUIX_GDK_PIXBUF_MODULE_FILES.
Fixes #1266.
Although currently happening, previously, syncthing-gtk would fail to open
with "Type RsvgHandle has already been registered". This was likely due to
various grafts as different librsvg would appear in environment variables
compared to syncthing-gtk references. This change fixed it at the time and
should help void it in the future.
* gnu/packages/syncthing.scm (syncthing-gtk)[arguments]{phases}: In wrap-libs
phase, also wrap with GUIX_GDK_PIXBUF_MODULE_FILES. Change GI_TYPELIB_PATH to
use suffix.
Change-Id: I2ae2e2ace5df5882b1cbdcd149cc0bc4823d3939