Undo the suppressing of xarray chunking warning

[veenstrajelmer]

The xarray chunking warning was suppressed in #679. However, significant performance improvements can be achieved if properly solving this: Deltares/xugrid#252

Todo:

• wait for new xugrid release including Merge partition chunks xugrid#253
• update minimal xugrid requirement (also relevant for from_meshkernel method: use all attributes xugrid#148)
• remove suppressing of the chunking warning again, although this was printed for each partition, not upon merging. It seems to have vanished though. Was it then indeed a mistake in xarray?
• check warnings in py3.9-mindeps and py3.12 pytest testcases
• solve remaintin warning in test_xarray_decode_default_fillvals