OCaml 5.4 support

[ajbt200128]

It seems like ppx_hash is dependent on ppxlib < 0.36.0, which is needed to support OCaml 5.4.

[mdelvecchio-jsc]

We are currently working internally on merging with OCaml 5.4, part of which involves upgrading the version of ppxlib we depend on. We will follow up with updates to our opam packages after the merge/upgrade completes.