test_imaging_mixins: ignore RuntimeWarning raised by numpy >= 1.24

[tobiasjj]

Why?
Numpy >= 1.24 raises a RuntimeWarning during casting if an floating point error occurs:
https://github.com/numpy/numpy/releases/tag/v1.24.0
numpy/numpy#21437

This causes test_imaging_mixins to fail:

The affected funtion is TiffExport.export_tiff()

Solution
Ignore the warning in the tests.

[rpauszek]

🚢

[JoepVanlier]

@rpauszek @tobiasjj I'm a bit late to the party, but isn't this warning us about an actual bug though?

Shouldn't the correct behavior be to explicitly clip prior to conversion if clip is True? Now the behaviour is undefined (I can't find anything in the numpy docs guaranteeing a particular behavior in the case of overflow). In my quick experiment it wraps around (which is is not what we want I think).

I also notice that the description in the RuntimeError is wrong. It mentions force=True while the argument is called clip.