Make dependency on KI18n and KTextWidgets explicit

They are already pulled in by KParts, but we better not rely on that
2 jobs for master in 8 minutes and 9 seconds (queued for 70 minutes and 10 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #103660

00:05:06

passed linux kf5-qt5 qt5.15 #103659

00:03:02

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