Fix TestCustomBuildSystemPlugin by readding .kdev4 folders of test data
Summary: Were accidentally removed in a5cee71e31330209d18d8dcd526078fb5b19b65f.
Reviewers: KDevelop, kfunk
Reviewed By: KDevelop, kfunk
Subscribers: kfunk, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D3996