postgresql: add dlSuffix to passthru

PostgreSQL changed the extension of its extensions in Darwin to use .dylib [1]

[1] b55f62abb2

pkgs/servers/sql/postgresql/default.nix

@@ -230,6 +230,8 @@ let
       withJIT = if jitSupport then this else jitToggle;
       withoutJIT = if jitSupport then jitToggle else this;
 
+      dlSuffix = if olderThan "16" then ".so" else stdenv.hostPlatform.extensions.sharedLibrary;
+
       pkgs = let
         scope = {
           postgresql = this;