Far-left demonstrators flew to Boston Monday to confront Sen. Kyrsten Sinema (D-Ariz.) over her opposition to the massive social spending bill being pushed by President Biden and Democratic congressional leaders — announcing their intention to do so as she ran the Boston Marathon. Just one problem: Sinema didn’t run the race. “While Kyrsten qualified for and attended the race, she could not run because of her continued recovery from a broken foot,” the senator’s spokesman John LaBombard told The Post in an email Monday night.