By Michael Holden and Kylie MacLellan LONDON (Reuters) – British police ended their investigation on Thursday into COVID-19 lockdown parties held at Prime Minister Boris Johnson’s Downing Street office, having handed out 126 fines in a scandal that had called into question his leadership. Johnson has faced widespread calls from opposition politicians and some in his own party for him to resign over the “partygate” scandal after it was revealed both he and officials had broken stringent laws his government had made. He and finance minister Rishi Sunak were both fined last month over a gathering…