Update libjpeg-turbo 3.0.0 for Qt 5.15.15

We need to make sure all security critical 3rd party modules (https://wiki.qt.io/Third_Party_Code_in_Qt) are the latest one before we can release. It seems libjpeg-turbo needs an update; we are using 2.1.5 but 3.0.0 is already available;

https://github.com/libjpeg-turbo/libjpeg-turbo/releases

Next release where this update is needed is Qt 5.15.15. This should be merged to tqtc/lts-5.15.15 by 31st of July. Please Pick-to: 5.15. 5.15.15