Delta Air Lines said it will add a nonbinary gender option for flight bookings later this year, becoming the third major carrier to provide a gender-neutral alternative and completing changes to its booking systems that the airline shelved during the pandemic. Atlanta-based Delta said last week it will add the “X” gender marker encouraged by the Transportation Security Administration for ticket purchases on the airline’s website, mobile app and at other purchasing locations. The shift comes amid a Biden administration effort to expand LGBTQ protections and broader measures by the U.S. Departme…