Fix GroupConfig.auto for permissions inventory

[nfx]

Fails when we don't have a match between workspace groups and account groups:

     84 toolkit = GroupMigrationToolkit(cfg)
---> 85 toolkit.prepare_environment()
     86 toolkit.cleanup_inventory_table()
     87 toolkit.inventorize_permissions()
...
    117 def prepare_environment(self):
--> 118     self._group_manager.prepare_groups_in_environment()
...
    173     logger.info("No group listing provided, all available workspace-level groups will be used")
    174     available_group_names = [g.display_name for g in self._workspace_groups]
--> 175     self._set_migration_groups(groups_names=available_group_names)
...
    120     backup_group = self._get_or_create_backup_group(source_group_name=name, source_group=ws_group)
    121     return MigrationGroupInfo(workspace=ws_group, backup=backup_group, account=acc_group)
--> 123 collected_groups = ThreadedExecution.gather(
    124     "get group info", [partial(get_group_info, group_name) for group_name in groups_names]
    125 )
    126 for g in collected_groups:
    127     self._migration_state.add(g)
...
    117 assert ws_group, f"Group {name} not found on the workspace level"
    118 acc_group = self._get_group(name, "account")
--> 119 assert acc_group, f"Group {name} not found on the account level"
    120 backup_group = self._get_or_create_backup_group(source_group_name=name, source_group=ws_group)
    121 return MigrationGroupInfo(workspace=ws_group, backup=backup_group, account=acc_group)