Mexico is on the brink of a historic change as forecasts indicate the first woman will be elected to the post of president in Sunday’s elections, the biggest in the nation’s history. Polling shows government candidate Claudia Sheinbaum from the ruling left-wing Morena party is the favourite, likely to win more votes than the opposition’s candidate Xóchitl Gálvez. A third presidential candidate is seen as having no chance. Sheinbaum, a climate scientist and former mayor of Mexico City, is considered a longtime ally of incumbent left-wing populist President Andrés Manuel López Obrador, who is no…