Templates need to be added to GitLab that allow to enable static compilation and testing on Windows and Linux platforms: https://invent.kde.org/sysadmin/ci-utilities/-/merge_requests/35, with subsequent related commits in master.

What this currently does is it compiles the libraries with -DBUILD_SHARED_LIBS=OFF and stores the artifacts in a separate cache location — separate from the other, dynamically-compiling CI jobs. For now, that location was seeded with the same Craft-packaged dependency libraries as the dynamic artifacts location is. That means that, at this time, the Qt binaries used by the static CI jobs in speech are still built dynamically. Ultimately, the goal is to have all of these libraries — as long as possible — to be available as static builds. See the discussion in the MR linked above for the context.