unison: fix build with ocamlPackages_4_09 (#82619)

Fixes #61867 and #61505, bumps the ocaml version unison is built
against to 4.08. The patches included here appear in the trunk version
of unison, but were not backported to 2.51.2.

pkgs/applications/networking/sync/unison/default.nix

@@ -27,6 +27,12 @@ stdenv.mkDerivation (rec {
     "UISTYLE=${if enableX11 then "gtk2" else "text"}"
   ] ++ stdenv.lib.optional (!ocaml.nativeCompilers) "NATIVE=false";
 
+  patches = [
+    # NOTE: Only needed until Unison 2.51.3 is released!
+    ./4.08-compatibility.patch
+    ./lablgtk.patch
+  ];
+
   preInstall = "mkdir -p $out/bin";
 
   postInstall = if enableX11 then ''