MNT: prepare h5netcdf backend for (coming) change in dimension handling (#6200)
MNT: prepare h5netcdf backend for (coming) change in dimension handling (#6200)

* prepare h5netcdf backend for (coming) change in dimension handling

* [test-upstream]
markelg/xray,jhamman/xarray,pydata/xarray,jhamman/xarray,pydata/xarray,pydata/xarray,markelg/xray,markelg/xray,jhamman/xarray