doas: fix recursive calls to doas

Doas was broken for recursive calls like `doas -u operator lncli`
where `lncli` internally calls doas.

modules/modules.nix

@@ -70,7 +70,8 @@ with lib;
       runAsUserCmd = mkOption {
         readOnly = true;
         default = if config.security.doas.enable
-                  then "doas -u"
+                  # TODO: Use absolute path until https://github.com/NixOS/nixpkgs/pull/133622 is available.
+                  then "/run/wrappers/bin/doas -u"
                   else "sudo -u";
       };
     };