Looking at the dasboard for StablePreview see here) seems to confirm this:
It is still failing with SlicerStable (see here) but I don't think we should put effort into it as we will soon release a new snapshot release and Slicer 5 is coming soon as well.
See: https://discourse.slicer.org/t/the-slicerdmri-extension-is-currently-unavailable/12276/11