Qt6 unittest failures

[Halla Rempt]

Currently the following tests fail for me when building with Qt6. I'm not sure how important these failures are.


These four seem to fail because of changes in QPainter. I first thought it was simply because we were comparing images with different colorspaces, but that's not the case. The differences are pretty subtle, and I'm not sure whether we should try to get the exact old results, or even whether that's possible.

         49 - libs-flake-TestSvgParser (Failed)
         50 - libs-flake-TestSvgParserCloned (Failed) 
         51 - libs-flake-TestSvgParserRoundTrip (Failed)
         276 - plugins-generators-KisScreentoneGeneratorTest (Failed) 

This one fails with the rects being different by 1, so I'm guess Qt6 rounds QRect transformations a bit different than it used to. I don't think it will lead to actual visual differences, though?
         
         191 - libs-image-kis_transform_mask_test (Failed) (QRect rounding changes)
         
This one needs more investigation, so I'm still looking into it. The qabstractitemmodeltester has consistently 0 rows instead of the expected number of rows.

        272 - plugins-dockers-storyboarddocker-StoryboardModelTest (Failed)         


These two always fail for me, also with Qt5:
        
        296 - plugins-impex-KisHeifTest (Failed)
        298 - plugins-impex-kis_jpegxl_test (Failed)