Make dependency on KI18n explicit

It already pulled in by KParts, but we better not rely on that
2 jobs for master in 22 minutes and 37 seconds (queued for 99 minutes and 45 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #103668

00:13:32

passed linux kf5-qt5 qt5.15 #103667

00:09:05

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