[Look And Feel KCM] Use new icon

Summary: Use the new icon for the Look And Feel KCM that was just added to breeze-icons. This icon will be available in Frameworks 5.55, which we can depend on for the 5.16 release.

Test Plan: {F6557534,size=full}

Reviewers: #vdg, davidedmundson

Reviewed By: davidedmundson

Subscribers: Codezela, davidedmundson, abetts, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18401