Make dependency on KI18n explicit

It already pulled in by KParts, but we better not rely on that
2 jobs for master in 5 minutes and 22 seconds (queued for 78 minutes and 14 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #103662

00:03:14

passed linux kf5-qt5 qt5.15 #103661

00:02:08

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