Summary:
m_imported was parented to the TestForeign class, which lasts for all
the tests. This caused an error on teardown.

Test Plan: Ran with ASAN. Finally everything passes!

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: plasma-devel, #frameworks

Tags: #frameworks, #plasma_on_wayland

Differential Revision: https://phabricator.kde.org/D9407