The white supremacist who shot to death 51 Muslims at two mosques in Christchurch , New Zealand, lost an attempt to abandon his guilty pleas at the country’s Court of Appeal on Thursday. The panel of three judges dismissed Brenton Tarrant’s claim that harsh prison conditions prompted his involuntarily admission to the terrorism, murder and attempted murder charges he faced. The Australian man, who is now 35, murdered 51 worshippers and injured dozens more in March 2019 when he drove to two Christchurch mosques and opened fire with semiautomatic weapons during Friday prayers. Tarrant’s guilty pleas in March 2020 brought relief to bereaved families and survivors of the attack, who dreaded the prospect of a lengthy trial and feared he would use it to air his hateful views. The failure of his appeal bid — which the court noted was made 505 days after the legal deadline for it to be filed — means such a trial has again been averted.…