Add basic test

src/oidc_test/settings.py

@@ -7,6 +7,7 @@ from pathlib import Path
 from pydantic import BaseModel, computed_field
 from pydantic_settings import (
     BaseSettings,
+    SettingsConfigDict,
     PydanticBaseSettingsSource,
     YamlConfigSettingsSource,
 )
@@ -42,8 +43,7 @@ class Settings(BaseSettings):
     oidc: OIDCSettings = OIDCSettings()
     secret_key: str = "".join(random.choice(string.ascii_letters) for _ in range(16))
 
-    class Config:
-        env_nested_delimiter = "__"
+    model_config = SettingsConfigDict(env_nested_delimiter="__")
 
     @classmethod
     def settings_customise_sources(