Reproduction of a Pydantic Setting bug where environment variables don't parse variables without prefixes

env_prefix_bug.py

import os

from pydantic import BaseModel, ValidationError

from pydantic_settings import BaseSettings, SettingsConfigDict

class Config(BaseSettings):
    model_config = SettingsConfigDict(env_prefix='my_prefix_', env_file=".env", extra="forbid")
    foo: list[str]

try:
    os.remove(".env")
except Exception:
    pass

# first: try parsing a list from an environment variable with a prefix
list_value = '["testy"]'
os.environ['my_prefix_foo'] = '["testy"]'
print("First Config", Config())
print("is list", isinstance(Config().foo, list))
# output:
# First Config foo=['testy']
# is list True
del os.environ['my_prefix_foo']
print("\n") 

# second: try parsing a list from an environment variable with a prefix
list_value = '["testy"]'
os.environ['foo'] = '["testy"]'
try:
    Config()
except ValidationError as e:
    print("Second Config:", e)
# output:
# Second Config: 1 validation error for Config
# foo
#   Input should be a valid list [type=list_type, input_value='["testy"]', input_type=str]
#     For further information visit https://errors.pydantic.dev/2.10/v/list_type
del os.environ['foo'] 
print("\n") 

# third: try parsing a list from a .env variable with a prefix
with open(".env", "w") as file:
    file.write(f"my_prefix_foo={list_value}")
print("Third Config", Config())
print("is list", isinstance(Config().foo, list))
# output
# Third Config foo=['testy']
# is list True
os.remove(".env")
print("\n") 

# fourth: try parsing a list from a .env variable WITHOUT a prefix
with open(".env", "w") as file:
    file.write(f"foo={list_value}")
try:
    Config()
except ValidationError as e:
    print("Fourth Config:", e)
# Fourth Config: 1 validation error for Config
# foo
#   Input should be a valid list [type=list_type, input_value='["testy"]', input_type=str]
#     For further information visit https://errors.pydantic.dev/2.10/v/list_type
os.remove(".env")