Pin Pydantic to <2.0 in build-environment.yml

[stephenmccalman]

Description

xeus-python-demo uses the latest pydantic, which is now v2.0. This appears to create an error in the build of the demo.

/home/runner/micromamba-root/envs/build-env/lib/python3.11/site-packages/jupyterlite_core/addons/__init__.py:69: UserWarning: [lite] [jupyterlite-xeus-python] failed to load: To define root models, use `pydantic.RootModel` rather than a field called '__root__'

While template will build and deploy (despite this error), the environment.yml's package (ipycanvas) is not available in the jupyterlite-xeus-python kernel (after launching the jupyterlite)

Pinning pydantic to <2.0 in the build-environment.yml will allow the demo to build and deploy properly.

Reproduce

Use to template to create a new demo.
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Context

• Browser and version: Chrome Version 114.0.5735.84

[stephenmccalman]

It appears that empack does not support Pydantic V2 yet.

https://docs.pydantic.dev/2.0/migration/
namely,

We have replaced the use of the root field to specify a "custom root model" with a new type called RootModel which is intended to replace the functionality of using a field called root in Pydantic V1.

[martinRenou]

Thanks for opening an issue! I'm moving it to empack