tests: disable test_run_modules::test_grainstats

[ns-rse]

The refactoring to use classes for objects rather than dictionaries breaks the topostats grainstats entry point that
was introduced with #1094.

Previously the dictionary item image=topostats_object["image"] was passed into processing.run_grainstats() when called from
processing.process_grainstats(). The refactoring requires that image_grain_crop=image_grain_crop, an object of the new type
ImageGrainCrops, is now passed to grainstats.

This isn't currently possible though because AFMReader loads .topostats objects and returns a dictionary and whilst
the refactoring does save the new image_grain_crop (/ImageGrainCrops) the loading does not currently re-create
these structures.

For now I have disabled the test of the entry point. Once this refactoring has been merged we will have to...

• Make TopoStats a dependency of AFMReader (somewhat wary of this as it may cause headaches further down the line
  but for now we'll go with it!).
• Modify AFMReader.topostats.load_topostats() to modify the data["grain_tensors"]["above"] and
  data["grain_tensors"]["above"] so that they are of class ImageGrainCrops (and the associated nested classes).
• Once that is done we can then pass the loaded data["grain_tensors"] to processing.run_grainstats() (this may
  require reconstructing to be the same as image_grain_crop, not sure at the moment!)

EDIT : Looking at this further we have a challenge as currently only the image_grain_crops.[above|below].full_mask_tensors are added to the topostats_object which means that when we load .topostats object it is not possible to create the ImageGrainCrops without first re-running the grain detection. This in turn means its not possible to have entry points for grainstats and all subsequent processing stages until we inlcude this data, at least in raw-format, when we save .topostats objects so that AFMReader can recreate them on loading.

I've noted this and more thoughts down in AFMReader #121.