Deprecation warning for platform dirs affecting downstream CI tests

[jasongrout]

This is going to be a bit rough:

https://github.com/ipython/ipython/actions/runs/3428540614/jobs/5712956265#step:7:76

We might be halting a lot of downstream CI builds by having a deprecation warning that essentially is on by default (which in a CI test is converted to an error).

Perhaps we delete the deprecation warning and figure out a lighter way to tell users about the upcoming new default. @blink1073, what do you think?

[blink1073]

We're already handling this in several other downstream consumers, e.g. https://github.com/jupyter-server/jupyter_server/blob/f6b732c652e0b5a600ff0d3f60c6a34173d8d6a5/pyproject.toml#L145. I think that is part of the responsibility of handling warnings as errors.