BEIJING—Boeing Co. raised its forecast slightly on Thursday for China’s aircraft demand for the next 20 years, betting on the country’s quick rebound from COVID-19 and future growth in its budget airline sector and e-commerce. Chinese airlines will need 8,700 new airplanes through 2040, 1.2 percent higher than its previous prediction of 8,600 planes made last year. Those would be worth $1.47 trillion based on list prices, the U.S. planemaker said in a statement. The 1.2 percent increase contrasted with the 6.3 percent growth Boeing forecast last year, which made China a bright spot in the aviation market at the height of coronavirus lockdowns worldwide. Earlier this month, Boeing revised up long-term forecasts for global airplane demand on the back of a strong recovery in commercial air travel in domestic markets like the United States. “There are promising opportunities to significantly expand international long-haul routes and air freight capacity,” said …