[Bug]: ImportError: cannot import name 'Undefined' from 'pydantic.fields'

Nobody has claimed this yet.

### Checklist

- [X] The issue exists after disabling all extensions
- [X] The issue exists on a clean installation of webui
- [ ] The issue is caused by an extension, but I believe it is caused by a bug in the webui
- [X] The issue exists in the current version of the webui
- [ ] The issue has not been reported before recently
- [ ] The issue has been reported before but has not been fixed yet

### What happened?

Fresh install gives error while starting

ImportError:
cannot import name 'Undefined' from 'pydantic.fields' (E:\StableDiffusion\stable-diffusion-webui-forge\venv\lib\site-packages\pydantic\fields.py)

### Steps to reproduce the problem

Fresh clone of the repo and starting the webui.bat

### What should have happened?

WegUI should start

### What browsers do you use to access the UI ?

_No response_

### Sysinfo

This gives the same error, also when dumping on the commandline

### Console logs

```Shell
stable-diffusion-webui-forge>webui.bat
venv "stable-diffusion-webui-forge\venv\Scripts\Python.exe"
Python 3.10.6 (tags/v3.10.6:9c7b4bd, Aug 1 2022, 21:53:49) [MSC v.1932 64 bit (AMD64)]
Version: f0.0.17v1.8.0rc-latest-276-g29be1da7
Commit hash: 29be1da7cf2b5dccfc70fbdd33eb35c56a31ffb7
Launching Web UI with arguments:
Total VRAM 24576 MB, total RAM 32689 MB
Set vram state to: NORMAL_VRAM
Device: cuda:0 NVIDIA GeForce RTX 3090 : native
Hint: your device supports --pin-shared-memory for potential speed improvements.
Hint: your device supports --cuda-malloc for potential speed improvements.
Hint: your device supports --cuda-stream for potential speed improvements.
VAE dtype: torch.bfloat16
CUDA Stream Activated: False

------------------------------------------------------------------------------------------------------------------------
launch.py 51
main()

launch.py 47 main
start()

launch_utils.py 541 start
import webui

webui.py 19
initialize.imports()

initialize.py 35 imports
import gradio # noqa: F401

__init__.py 3
import gradio.components as components

__init__.py 1
from gradio.components.annotated_image import AnnotatedImage

annotated_image.py 13
from gradio.components.base import IOComponent, _Keywords

base.py 20
from fastapi import UploadFile

__init__.py 7
from .applications import FastAPI as FastAPI

applications.py 15
from fastapi import routing

routing.py 22
from fastapi import params

params.py 4
from pydantic.fields import FieldInfo, Undefined

ImportError:
cannot import name 'Undefined' from 'pydantic.fields' (stable-diffusion-webui-forge\venv\lib\site-packages\pydantic\fields.py)
```

### Additional information

GPU drivers are up up to date

Start by reproducing the failure with webui.bat and read the import chain through launch.py, launch_utils.py, webui.py, initialize.py, and the FastAPI traceback. Check the installed FastAPI and Pydantic versions involved in the failing import. Done means a fresh installation can start the web UI without the Undefined import error.

Written by the indexing model from the issue text.