ci: Require tests to pass only on Linux

Vlad Zahorodniirequested to merge
work/cherry-pick-354d4f78 into Plasma/6.2

FreeBSD CI is unstable and we lack people who have relevant knowledge about FreeBSD to debug and address the issue.

(cherry picked from commit 354d4f78)

Co-authored-by: Vlad Zahorodnii vlad.zahorodnii@kde.org

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