casadi: set meta.platforms

To try to see why why nixpkgs-review does not list casadi on aarch64-darwin

We still can see
`165/165 Test #165: example-py-casadi-quadrotor-ocp ............  Passed`
in `nix log .#python3Packages.pinocchio` on aarch64-darwin, so
everything looks fine anyways.

pkgs/by-name/ca/casadi/package.nix

@@ -213,5 +213,6 @@ stdenv.mkDerivation (finalAttrs: {
     homepage = "https://github.com/casadi/casadi";
     license = lib.licenses.lgpl3Only;
     maintainers = with lib.maintainers; [ nim65s ];
+    platforms = lib.platforms.all;
   };
 })