nixos/postgresql: fix enableJIT = false

The enableJIT = true case was fixed in #221851 or
e2fb651752 respectively.

However this did not take the case into consideration, when doing this:

    services.postgresql = {
      enable = true;
      enableJIT = false;
      package = pkgs.postgresql_15_jit;
    };

If enableJIT is treated as the source of truth, then this should indeed
cause JIT to be disabled, which this commit does.

nixos/modules/services/databases/postgresql.nix

@@ -14,7 +14,7 @@ let
       #     package = pkgs.postgresql_<major>;
       #   };
       # works.
-      base = if cfg.enableJIT then cfg.package.withJIT else cfg.package;
+      base = if cfg.enableJIT then cfg.package.withJIT else cfg.package.withoutJIT;
     in
     if cfg.extraPlugins == []
       then base