ocaml-5: bump magic number to match 5.0.0~alpha0

[jmid]

This PR bumps the magic numbers in the caml-5 branch to suffix 32 to match the upcoming 5.0.0 ones: ocaml/ocaml@293014b. Without it, the caml-5 branch will fail on 5.0.0~alpha0:

$ cat hello.ml 
let _ = print_endline "hello, world!"
$ ocamlc -o hello.byte hello.ml
$ js_of_ocaml hello.byte 
js_of_ocaml: Error: Bytecode version mismatch.
js_of_ocaml: Error: Your ocaml bytecode and the js_of_ocaml compiler have to be compiled with the same version of ocaml.
js_of_ocaml: Error: The Js_of_ocaml compiler has been compiled with ocaml version 5.0.0~alpha0.
js_of_ocaml: Error: Its seems that your ocaml bytecode has been compiled with a newer version of ocaml.

[hhugo]

Thanks. This MR should target the master branch, not the ocaml-5 one.

[jmid]

Ah, sorry about that! 🙏
Later yesterday I realized that some OCaml 5.0 support was already merged in #1265 and that ocaml-5 is part of #1262
(I'm unsure of the relation between the two PRs though).

I'll close this one and open one against master.

[jmid]

Second attempt in #1288 😁