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Summary:
While I'm stuck with https://bugs.kde.org/show_bug.cgi?id=420324, I might as well make
the spurious "no network connectivity" message prettier and more standardized by using the
new Kirigami cimponent introduced in D29057.

Depends on D29057

Test Plan: {F8251669}

Reviewers: #vdg, #discover_software_store, apol

Reviewed By: #discover_software_store, apol

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D29059