[applets/taskmanager] increase size of tooltip playback ToolButton sizes

Summary: Per VDG mockup.

Test Plan:
Before: {F8090890}

After: {F8090880}

Reviewers: #vdg, manueljlin

Reviewed By: #vdg, manueljlin

Subscribers: ndavis, plasma-devel

Tags: #plasma

Maniphest Tasks: T12640

Differential Revision: https://phabricator.kde.org/D27222