Merge pull request #155962 from NixOS/containers-bootloader

nixos/container-config: Only use `true` as fallback

nixos/modules/virtualisation/container-config.nix

@@ -18,7 +18,7 @@ with lib;
     services.openssh.startWhenNeeded = mkDefault true;
 
     # Shut up warnings about not having a boot loader.
-    system.build.installBootLoader = "${pkgs.coreutils}/bin/true";
+    system.build.installBootLoader = lib.mkDefault "${pkgs.coreutils}/bin/true";
 
     # Not supported in systemd-nspawn containers.
     security.audit.enable = false;