By Muvija M LONDON (Reuters) -More than 115,000 postal workers at Royal Mail have voted to strike over pay, trade union CWU said on Tuesday, putting them on course for what could be the biggest industrial action to hit Britain this summer. Rising inflation and stagnant real wage growth has forced unions across ports, railways and airlines to strike or trigger industrial action as Britain faces its worst cost-of-living crisis in decades. Royal Mail had offered a pay rise of 5.5% for CWU-grade workers, which it described as its biggest increase in years. Inflation is forecast to reach 11% this y…