Sam Altman, chief executive officer of OpenAI, during an event in Seoul, South Korea, on Friday, June 9, 2023.SeongJoon Cho | Bloomberg | Getty ImagesOpenAI is allowing employees to sell roughly $1.5 billion worth of shares in a new tender offer to SoftBank, CNBC has learned.The new financing will allow the Japanese tech conglomerate to get an even larger slice of the AI startup, and it will allow current and former OpenAI employees to cash out their shares, two people familiar with the matter t...