nixos/os-release: make default_hostname distribution default (#359571)

Author: jopejoe1

nixos/modules/misc/version.nix

@@ -41,7 +41,7 @@ let
       IMAGE_VERSION = optionalString (config.system.image.version != null) config.system.image.version;
       VARIANT = optionalString (cfg.variantName != null) cfg.variantName;
       VARIANT_ID = optionalString (cfg.variant_id != null) cfg.variant_id;
-      DEFAULT_HOSTNAME = config.networking.fqdnOrHostName;
+      DEFAULT_HOSTNAME = config.system.nixos.distroId;
       SUPPORT_END = "2025-06-30";
     };