misc/py-openai: update runtime dependency on py-pydantic to py-pydantic2

misc/py-shell-gpt (one of the dependent ports on py-openai) has the
following dependency graph:

misc/py-shell-gpt -> misc/py-instructor -> devel/py-pydantic2

   (pyproject.toml contains pydantic = "^2.0.2")
-> misc/py-openai -> devel/py-pydantic
   (pyproject.toml contains "pydantic>=1.9.0, <3")

Updating the dependency of py-openai to py-pydantic2 satisfies both
requirements at the same time.

PR: 276548
Approved by: yuri (maintainer)