As America stumbles to the end of its second year of living with Covid, it’s heartening to see the return of those much-anticipated holiday traditions that keep us feeling almost normal. The Macy’s Thanksgiving Day Parade returned last month in pre-pandemic splendor, for instance. Two weeks ago, the lights flickered to life on the Rockefeller Center tree. And this Sunday at 7:30 p.m. ET, PBS will air A Charlie Brown Christmas, which millions of Americans have watched annually since its 1965 debut.