upgrade_initramfs_gen: fix wrong field name on livemode config

repos/system_upgrade/common/actors/initramfs/upgradeinitramfsgenerator/libraries/upgradeinitramfsgenerator.py

@@ -542,7 +542,7 @@ def process():
 
         with mounting.mount_upgrade_iso_to_root_dir(userspace_info.path, target_iso):
             prepare_userspace_for_initram(context)
-            if livemode_config and livemode_config.enabled:
+            if livemode_config and livemode_config.is_enabled:
                 boot_file_info = prepare_boot_files_for_livemode(context)
             else:
                 boot_file_info = generate_initram_disk(context)