CHICAGO—United Airlines Holdings on Wednesday trimmed its capacity forecast and warned of higher costs, after posting a smaller-than-expected fourth-quarter loss, citing turbulence from the Omicron coronavirus variant. The Chicago-based carrier said the latest wave of the health crisis has depressed near-term demand even as bookings for the spring and beyond remain strong. United said its priority is to match capacity with demand. As a result, its 2022 capacity is now projected to be lower than in 2019, instead of growing 5 percent as estimated earlier. It expects to restore 82 percent to 84 percent of pre-pandemic capacity in the quarter through March, with revenue recovering to just 75 percent to 80 percent of 2019 levels. Costs this year are now expected to be higher than in 2019, instead of going down. United’s shares declined about 2.5 percent to $43.31 in extended trading. Rival Delta Air Lines last week forecast a …