[SDDM theme] Update the theme preview

Summary: The current preview of our Breeze SDDM theme is outdated. This patch adds a new and updated preview.

Test Plan:
Before:
{F6529783}

After:
{F6529784}

Reviewers: #plasma, #vdg, #breeze, GB_2

Reviewed By: #vdg, GB_2

Subscribers: GB_2, oussemabouaneni, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18012