Cabal/Stack initialBuildSteps Breakage (Part 2)

Stack version 2.15.7 was made available via GHCup yesterday. It took some time due to an unrelated issue. I confirmed that the initialBuildSteps issue is resolved locally, but then my CI jobs failed because Haskell Actions has not been configured with that new version yet. One can explicitly request the new version (instead of using latest), in which case it is installed using GHCup, to work around the issue. I created a pull request, notifying the developers that the new version is required for GHC 9.10.1 support.