CI: caching the subprojects breaks CI for MRs with new subprojects
The CI of merge requests that introduce a new subproject fail because the warp subproject isn't downloaded and only a cached version is used. The subprojects are downloaded when building the docker images via this script https://gitlab.gnome.org/GNOME/gnome-software/-/blob/master/.gitlab-ci/cache-subprojects.sh
For example the MR !416 (closed) fails because of this issue.