librest_1_0: propagate dependencies from Requires

pkg-config will not be able to find rest-1.0 otherwise.

pkgs/development/libraries/librest/1.0.nix

···
     gobject-introspection
   ];
 
-  buildInputs = [
+  propagatedBuildInputs = [
     glib
     json-glib
     libsoup_3