Cassie Bowden can’t trust her own memories, so why would she trust anyone else? The heroine of “The Flight Attendant,” returning to HBO Max Thursday for its second season, sees spies everywhere. She sees dead one night stands who talk to her, body doubles who frame her for murder and three versions of herself in her mind. Her work friend turned out to be a CIA agent and another was spying for North Korea. It’s hard to blame Cassie (Kaley Cuoco) for being hesitant about everyone in her life. “Everyone has a secret. You have a secret, they have a secret, everyone has a secret. But I don’t think …