ocaml 5: restrict posixat

Same as 0a4351c

Author: dc-mak

packages/posixat/posixat.v0.16.0/opam

@@ -10,7 +10,7 @@ build: [
   ["dune" "build" "-p" name "-j" jobs]
 ]
 depends: [
-  "ocaml"         {>= "4.14.0"}
+  "ocaml"         {>= "4.14.0" & < "5.0"}
   "base"          {>= "v0.16" & < "v0.17"}
   "ppx_optcomp"   {>= "v0.16" & < "v0.17"}
   "ppx_sexp_conv" {>= "v0.16" & < "v0.17"}