Mark the winning team.

def _set_winning_team(self):
        """Mark the winning team."""
        if not self._summary['finished']:
            return
        for team in self._summary['diplomacy']['teams']:
            team['winner'] = False
            for player_number in team['player_numbers']:
                for player in self._summary['players']:
                    if player_number == player['number']:
                        if player['winner']:
                            team['winner'] = True