Fix misaligned numbers on subscription list

Summary:
Unread and total articles were aligned to top instead of center.

Test Plan:
Before: {F5816392, size=full}
After: {F5816393, size=full}

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: mlaurent, #kde_pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D12406