ocamlPackages.ppx_cstruct: disable tests for OCaml ≥ 5.1

pkgs/development/ocaml-modules/cstruct/ppx.nix

···
-{ lib, buildDunePackage, cstruct, sexplib, ppxlib
+{ lib, buildDunePackage, ocaml, cstruct, sexplib, ppxlib
 , ocaml-migrate-parsetree-2
 , ounit, cppo, ppx_sexp_conv, cstruct-unix, cstruct-sexp
 }:
···
 
     propagatedBuildInputs = [ cstruct ppxlib sexplib ];
 
-    doCheck = true;
+    doCheck = !lib.versionAtLeast ocaml.version "5.1";
     nativeCheckInputs = [ cppo ];
     checkInputs = [ ounit ppx_sexp_conv cstruct-sexp cstruct-unix ocaml-migrate-parsetree-2 ];
   }