Add deprecated flag to mehari-eio-unix.

Author: ArtichOwO

packages/mehari-eio-unix/mehari-eio-unix.0.1/opam

@@ -6,6 +6,7 @@ authors: ["The mehari programmers"]
 license: "LGPL-3.0-or-later"
 homepage: "https://github.com/Psi-Prod/Mehari"
 bug-reports: "https://github.com/Psi-Prod/Mehari/issues"
+flags: deprecated
 depends: [
   "dune" {>= "2.9"}
   "ocaml" {>= "5.0.0"}