fix RetrievalMethod StrEnum (#26768)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

api/services/entities/model_provider_entities.py

@@ -1,5 +1,5 @@
 from collections.abc import Sequence
-from enum import Enum
+from enum import StrEnum
 
 from pydantic import BaseModel, ConfigDict, model_validator
 
@@ -27,7 +27,7 @@ from core.model_runtime.entities.provider_entities import (
 from models.provider import ProviderType
 
 
-class CustomConfigurationStatus(Enum):
+class CustomConfigurationStatus(StrEnum):
     """
     Enum class for custom configuration status.
     """