testsuite: disable testfork.ml on OpenBSD
testsuite: disable testfork.ml on OpenBSD

gerdstolpmann/ocaml,yunxing/ocaml,yunxing/ocaml,gerdstolpmann/ocaml,eliberis/ocaml,yunxing/ocaml,yunxing/ocaml,eliberis/ocaml,msprotz/ocaml,msprotz/ocaml,yunxing/ocaml,msprotz/ocaml,eliberis/ocaml,eliberis/ocaml,msprotz/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,eliberis/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml