Unknown value for enum

### Summary

Unknown value for enum error in from_json

### Reproduction Steps

```protobuf
syntax = "proto3";

package hello;

enum Test {
TestUnset = 0;
Test1 = 1;
Test2 = 2;
}

message Greeting {
repeated Test test = 1;
}
```

```python
# Generated by the protocol buffer compiler. DO NOT EDIT!
# sources: test.proto
# plugin: python-betterproto
# This file has been @generated

from dataclasses import dataclass
from typing import (
List,
)

import betterproto

class Test(betterproto.Enum):
TestUnset = 0
Test1 = 1
Test2 = 2

@dataclass(eq=False, repr=False)
class Greeting(betterproto.Message):
test: List["Test"] = betterproto.enum_field(1)
```

```python
import hello
JSON_STR = """
{
"test": [1]
}
"""
greeting = hello.Greeting().from_json(JSON_STR)
```

### Expected Results

Should parse correct

### Actual Results

```
File "/opt/homebrew/Caskroom/miniconda/base/envs/platform/lib/python3.12/site-packages/betterproto/__init__.py", line 1690, in from_json
return self.from_dict(json.loads(value))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Caskroom/miniconda/base/envs/platform/lib/python3.12/site-packages/betterproto/__init__.py", line 1630, in from_dict
for field, value in self._from_dict_init(value).items():
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Caskroom/miniconda/base/envs/platform/lib/python3.12/site-packages/betterproto/__init__.py", line 1581, in _from_dict_init
value = [enum_cls.from_string(e) for e in value]
^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Caskroom/miniconda/base/envs/platform/lib/python3.12/site-packages/betterproto/enum.py", line 202, in from_string
raise ValueError(f"Unknown value {name} for enum {cls.__name__}") from e
ValueError: Unknown value 1 for enum Test
```

### System Information

libprotoc 29.3
Python 3.12.9
Name: betterproto
Version: 2.0.0b7
Summary: A better Protobuf / gRPC generator & library
Home-page: https://github.com/danielgtaylor/python-betterproto
Author: Daniel G. Taylor
Author-email: danielgtaylor@gmail.com
License: MIT
Location: /opt/homebrew/Caskroom/miniconda/base/envs/platform/lib/python3.12/site-packages
Requires: grpclib, python-dateutil, typing-extensions
Required-by: platform-sdk

### Checklist

- [x] I have searched the issues for duplicates.
- [x] I have shown the entire traceback, if possible.
- [x] I have verified this issue occurs on the latest prelease of betterproto which can be installed using `pip install -U --pre betterproto`, if possible.

Bắt đầu trong betterproto/__init__.py tại _from_dict_init và lần theo lệnh gọi của nó đến betterproto/enum.py: from_string, như được hiển thị trong traceback. Tái hiện trường hợp enum lặp lại bằng protobuf và JSON được cung cấp, sau đó xác minh rằng các giá trị enum dạng số được phân tích thành công từ from_json mà không làm hỏng việc xử lý chuỗi.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.