KDiff3 windows build failing

[Michael Reeves]

I recently updated KDiff3 to depend on Boost::signal2. This is part of the
Boost-headers package. However craft is refusing to download this
dependency after updating my blue print
https://invent.kde.org/kde/craft-blueprints-kde/-/commit/5dbe69727e7be065ad2e61c840d0052b83b4a1f8.
Am I missing something?