Improve app icon padding on Application page

Summary: Make the padding to the right of the app icon the same as its left padding.

Test Plan:
Tested in KDE Neon. Before:
{F5669005}

After:
{F5669006}

Reviewers: apol, andreaska, #discover_software_store, #vdg, andreask

Reviewed By: apol, #discover_software_store, andreask

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10021