assert qt and kf5 versions against their actual underlying value

Summary:
this isn't super useful to compare other than the calls don't explode,
doesn't have a downside either though...

Test Plan: test still passes

Reviewers: tcanabrava

Reviewed By: tcanabrava

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D22232