Reconsider the zarr remote load test #188
Description
This seems to intermittently fail for odd reasons -- presumably because the taget server is somewhat unreliable.
Most recently, we have had it pass the availability test when requesting the "...zarr3" url (? the directory?), but then go on to fail fetching .zarr3/.zattrs or .zarr3/.zmetadata.
Hence this change (proposed in #187).
But all this is a bit awkward, and perhaps we could migrate to a more reliable online dataset?