By Andrius Sytas RIGA (Reuters) -The centre-right New Unity party of Latvian Prime Minister Krisjanis Karins was set to win Saturday’s national election, an exit poll showed, after a campaign dominated by security concerns following Russia’s invasion of Ukraine. If confirmed, the result should mean Latvia remains a leading voice alongside its Baltic neighbours Lithuania and Estonia in pushing the European Union for a decisive stance against Russia. But it could widen a rift between the country’s Latvian majority and its Russian-speaking minority over their place in society, amid widespread nat…