Fix warning

Summary: .../share/plasma/shells/org.kde.plasma.desktop/contents/applet/AppletError.qml:33:5: QML IconItem: Detected anchors on an item that is managed by a layout. This is undefined behavior; use Layout.alignment instead.

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13523