Junior fixes for KTechLab: fixing warnings of deprecated API

[Zoltan Padrah]

Hi,

I have seen that on the Continuous Integration (CI) systems at KDE
there are quite a few build warnings about usage of deprecated Qt /
KDE APIs. For example see the log from below:

https://invent.kde.org/sdk/ktechlab/-/jobs/416638

Fixing these warnings should be quite straightforward, most warnings
even show suggestions about what would be a possible fix.

In case someone would like to get familiar with KTechLab ot KDE or Qt
development, feel free to send merge requests with fixes to these
warnings.

Best regards,

 Zoltan