Replace nil with null in helm chart

[bstadlbauer]

We've just tried to deploy the 2022.7.0 version of the helm chart and ran into:

Handler 'daskworkergroup_replica_update/spec.worker.replicas' failed with an exception. Will retry.
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/kopf/_core/actions/execution.py", line 276, in execute_handler_once
    result = await invoke_handler(
  File "/usr/local/lib/python3.10/site-packages/kopf/_core/actions/execution.py", line 371, in invoke_handler
    result = await invocation.invoke(
  File "/usr/local/lib/python3.10/site-packages/kopf/_core/actions/invocation.py", line 116, in invoke
    result = await fn(**kwargs)  # type: ignore
  File "/usr/local/lib/python3.10/site-packages/dask_kubernetes/operator/controller/controller.py", line 639, in daskworkergroup_replica_update
    batch_size = min(workers_needed, SIZE) if SIZE else workers_needed
TypeError: '<' not supported between instances of 'str' and 'int'

We're currently testing whether settings things to null fixes this. cc @dyu-bot

[jacobtomlinson]

Thanks @bstadlbauer. I've just tagged 2023.7.1 with this fix in.

[dyu-bot]

Thanks for the quick release @jacobtomlinson

[dyu-bot]

Actually @jacobtomlinson it's still failing to create workers with the new release.

I believe because here the env variable must be a string. So need to cast these