Dataflow jobs require specific Zarr version

[raspstephan]

I ran into issues running jobs on Dataflow resulting in the following error:

AttributeError: Can't get attribute 'Array' on <module 'zarr.core' from '/opt/apache/beam-venv/beam-venv-worker-sdk-0-0/lib/python3.11/site-packages/zarr/core/__init__.py'

Setting zarr==2.18.4 in setup.py solved this issue. Since I don't fully understand the cause of this and am not sure it is reproducible by others, I decided to not change the default in setup.py but hopefully this issue helps others if they run into it as well.