apparent breaking change in DotEnvSettingsSource when extra="allow"

[zzstoatzz]

a breaking change to how DotEnvSettingsSource handles setting values from an .env file when the settings config has extra='allow' seems to have been introduced with 2.2.0 via #221

In particular, it seems that env_prefix now remains present on the "extra" setting attribute name instead of being removed as it was before 2.2.0

I will take a stab at a fix

MRE

» tree -a
.
├── .env
└── settings.py

settings.py

from pydantic_settings import BaseSettings, SettingsConfigDict

class FooSettings(BaseSettings):
    model_config = SettingsConfigDict(
        extra="allow",
        env_file=".env",
        env_prefix="foo_"
    )
    
    x: str

settings = FooSettings()

print(f'{getattr(settings, "y", None)=}')
print(f'{getattr(settings, "foo_y", None)=}')

.env

FOO_X=something
FOO_Y=something_else

on 2.2.0

(pydantic-settings-2dot2) pad-2 :: src/open-source/mre
» python settings.py
getattr(settings, "y", None)=None
getattr(settings, "foo_y", None)='something_else'

» pip list | rg settings
pydantic-settings 2.2.0

on 2.1.0

(pydantic-settings-2dot1) pad-2 :: src/open-source/mre
» python settings.py
getattr(settings, "y", None)='something_else'
getattr(settings, "foo_y", None)=None

» pip list | rg settings
pydantic-settings 2.1.0