Income investors, beware.Walgreens Boots Alliance (WBA -3.15%) did something last week it hasn't done in quite a while: It made shareholders happy.The big pharmacy retailer and wholesaler announced in its fiscal 2024 fourth-quarter update that it plans to close around 1,200 stores over the next three years. The news caused Walgreens' shares to deliver the biggest gain so far in 2024. Despite Walgreens' recent bounce, the company still faces considerable uncertainty. Income investors especially have reason t ...