Fix test and update dependencies

[clarasb]

This PR:

• Fixes test
• Updates dependecies:
  • from h5netcdf to h5netcdf[h5py] to ensure the HDF5 backend required by NetCDF tests is installed
  • constrain xarray version to <2026.4 to retain compatibility with Zarr 2.

Note: failing tests get fixed by PR #109

---

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.92%. Comparing base (3256d37) to head (3ed30f6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #110   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          30       30           
  Lines        1418     1418           
=======================================
  Hits         1417     1417           
  Misses          1        1           

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