QT Build issue under Windows

https://github.com/compiler-explorer/infra/actions/runs/15001645629/job/42149903629

QT builds in most situations, but script determines the needed binaries are not available. Need to debug and investigate.

Start with the linked GitHub Actions job log for the Windows build and identify where the script decides that the required Qt binaries are unavailable. Trace that decision through the build workflow; done means the failure is reproduced and the binary-detection behavior is corrected or clearly explained.

Written by the indexing model from the issue text.