Apna, a 21-month-old startup that is helping millions of blue- and gray-collar workers in India upskill themselves, find communities and land jobs, is inching closer to becoming the fastest tech firm in the world’s second-largest internet market to become a unicorn. Tiger Global is in advanced stages of talks to lead a $100 million round in Apna, according to four sources familiar with the matter. The proposed terms value the startup at over $1 billion, the sources said. The round hasn’t closed yet, so terms of the deal may change,…