BERLIN, June 22 (Reuters) - Outgoing British Prime Minister Keir Starmer announced his departure on Monday amid plunging approval ratings, but there were warm words from European leaders who had generally found him easier to work with than his recent predecessors. Starmer, the first non-Conservative prime minister since Britain voted to leave the European Union, rejected suggestions that it could rejoin the 27-member bloc, but he had pushed to i…