(Reuters) – Protesters took to the streets as Belarus held a referendum on Sunday to adopt a new constitution that would ditch its non-nuclear status at a time when the country has become a launchpad for Russian troops invading Ukraine. The vote, almost certain to pass under the tightly controlled rule of President Alexander Lukashenko, could see nuclear weapons on Belarusian soil for the first time since the country gave them up after the fall of the Soviet Union. It raises the stakes at a time when Lukashenko has fallen behind Russian President Vladimir Putin’s military assault on Ukraine af…