[Device Notifier] Fix action button vertical alignment

Test Plan:
Before
{F6462112}

After
{F6462113}

Reviewers: #vdg, ngraham

Reviewed By: #vdg, ngraham

Subscribers: abetts, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D17420