chore: pin pydantic version to avoid a reasoning engine failure

[vishwarajanand]

Reasoning engine is failing in #283 hence this PR is needed to fix the tests.

Without this change, the tests in reasoning engine fail: test log saying:

NameError: name 'SafetySetting' is not defined. Did you mean: 'SafetySettingsType'?

which is caused due to below exception:

  File "/builder/home/.local/lib/python3.11/site-packages/pydantic/_internal/_generate_schema.py", line 1229, in _common_field_schema
    raise PydanticUndefinedAnnotation.from_name_error(e) from e
pydantic.errors.PydanticUndefinedAnnotation: name 'SafetySetting' is not defined

With this change, the tests in reasoning engine pass: test log.

Relevant issue in langchain repo: langchain-ai/langchain#28271