Use more appropriate icon that's colorful at small sizes

The current icon does not follow the recommended pattern of using preferences- icons
and has a small version that's monochrome, causing the sidebar in System Settings to
inappropriately display some small monochrome icons.

Ref T10165
2 jobs for master in 18 minutes and 23 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #16710
linux kf5-qt5 qt5.12

00:06:35

34.0%
passed #16711
windows
windows kf5-qt5 qt5.13

00:18:22