Limit Dask Distributed version to <2023.4

Avoid problems with serialising h5py objects in task graphs,  introduced
in 2023.4.0.

See https://distributed.dask.org/en/stable/changelog.html#v2023-4-0
and dask/distributed#7564 for details.

setup.cfg

@@ -30,10 +30,10 @@ project-urls =
 [options]
 include_package_data = True
 install_requires =
-    dask[array,diagnostics,distributed] != 2021.3.*
+    dask[array,diagnostics,distributed]!=2021.3.*,<2023.4
     h5py>=3.8
     hdf5plugin>=4.0.1
-    nexgen >= 0.7.2
+    nexgen>=0.7.2
     numpy
     pandas
     pint