gfile: Use a more specific error message if symlinks are not supported
gfile: Use a more specific error message if symlinks are not supported

The string is already translated in `GLocalFile`, so this doesn’t
introduce a new translatable string.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib