Alyson Hannigan still can’t bring herself to watch the ‘How I Met Your Mother’ spin-off series. The 50-year-old actress played Lily Aldrin on the TV sitcom between 2005 and 2014 – but Alyson has never watched any episodes of the spin-off show, ‘How I Met Your Father’. The actress told PEOPLE: “I should have [watched]. But I just couldn’t. “It just made me sad because I’m like, oh, that’s the same set.” Alyson still has very fond memories of filming the final season of ‘How I Met Your Mother’. The actress – who starred on the hit TV show alongside the likes of Jason Segel, Cobie Smulders and Ne…