A small button appears next to shop buttons that allows you to promote your units needed for victory, without actually buying them. Previously, you had to buy and then sell the unit if you didn't actually want it, but needed it to win the game. Now you can just click this new button, claim victory progress and move on.

Also in the Victory window (Hotkey V), there is now a checkbox to hide units you've promoted already toward reaching a win. You can click this button and it will only show units you still need to win.