Try to avoid aliasing with system fonts

The rendernode parser creates its own fontmap for the fonts that
we deserialize from blobs. But we were using the system fontconfig
configuration for it, leading to system fonts still being found.
This is bad, and causes test failures in ci. Try with an empty
fontconfig configuration instead.

gsk/gskrendernodeparser.c

@@ -1005,7 +1005,7 @@ ensure_fontmap (Context *context)
 
   context->fontmap = pango_cairo_font_map_new ();
 
-  config = FcInitLoadConfig ();
+  config = FcConfigCreate ();
   pango_fc_font_map_set_config (PANGO_FC_FONT_MAP (context->fontmap), config);
   FcConfigDestroy (config);