chore: pin pydantic version for mypy

[RogerHYang]

This fixes following mypy error on github CI. Potential cause.

/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/openai/_models.py:408: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Traceback (most recent call last):
Please report a bug at https://github.com/python/mypy/issues
File "mypy/semanal.py", line 6475, in accept
version: 1.5.1
/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/openai/_models.py:408: : note: use --pdb to drop into pdb
File "mypy/nodes.py", line 1141, in accept
File "mypy/semanal.py", line 1600, in visit_class_def
File "mypy/semanal.py", line 1685, in analyze_class
File "mypy/semanal.py", line 1714, in analyze_class_body_common
File "mypy/semanal.py", line 1801, in apply_class_plugin_hooks
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 187, in _pydantic_model_class_maker_callback
return transformer.transform()
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 478, in transform
self.add_initializer(fields, config, is_settings, is_root_model)
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 856, in add_initializer
args = self.get_field_arguments(
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 1038, in get_field_arguments
arguments = [
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 1039, in
field.to_argument(
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 346, in to_argument
variable=self.to_var(current_info, use_alias),
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 373, in to_var
return Var(name, self.expand_type(current_info))
File "/home/runner/.local/share/hatch/env/virtual/arize-phoenix/C8K4HrkP/type/lib/python3.8/site-packages/pydantic/mypy.py", line 362, in expand_type
raise _DeferAnalysis()
_DeferAnalysis:
Error: Process completed with exit code 2.