tests: use mkDefault with enable

We shouldn't need to mkForce every tests attempt to configure this
value.

tests/default.nix

@@ -92,7 +92,7 @@ let
 
       # Fix impurities. Without these some of the user's environment
       # will leak into the tests through `builtins.getEnv`.
-      xdg.enable = true;
+      xdg.enable = lib.mkDefault true;
       home = {
         username = "hm-user";
         homeDirectory = "/home/hm-user";

tests/modules/misc/xdg/default-locations.nix

@@ -1,7 +1,7 @@
 { config, lib, ... }: {
   config = {
     # Test fallback behavior for stateVersion >= 20.09, which is pure.
-    xdg.enable = lib.mkForce false;
+    xdg.enable = false;
     home.stateVersion = "20.09";
 
     xdg.configFile.test.text = "config";

tests/modules/programs/k9s/empty-settings.nix

@@ -3,7 +3,7 @@
 {
   programs.k9s.enable = true;
 
-  xdg.enable = lib.mkIf pkgs.stdenv.isDarwin (lib.mkForce false);
+  xdg.enable = lib.mkIf pkgs.stdenv.isDarwin false;
 
   nmt.script = let
     configDir = if !pkgs.stdenv.isDarwin then

tests/modules/programs/k9s/example-settings.nix

@@ -1,7 +1,7 @@
 { config, pkgs, lib, ... }:
 
 {
-  xdg.enable = lib.mkIf pkgs.stdenv.isDarwin (lib.mkForce false);
+  xdg.enable = lib.mkIf pkgs.stdenv.isDarwin false;
 
   programs.k9s = {
     enable = true;