Avoid needlessly converting a QIcon to a pixmap

We can pass a QIcon directly here, which is better since it makes the widget responsible for picking the correct icon size
2 jobs for master in 14 minutes and 2 seconds (queued for 63 minutes and 4 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #103650

00:09:39

passed linux kf5-qt5 qt5.15 #103649

00:04:23

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