MILAN (Reuters) – Exor, the holding company of Italy’s Agnelli family, said on Thursday it had agreed to increase by $328 million the cash price it would receive for the planned sale of its PartnerRe reinsurer thanks to its solid performance last year. Exor last year signed an agreement to sell PartnerRe to French insurance group Covea for $9 billion, reviving a deal that had been derailed by the coronavirus pandemic. The holding company on Thursday said in a statement from its full-year results that, based on PartnerRe’s common shareholders’ equity at the end of last year, “the agreed cash co…