Pydantic fails to read content of files in secrets_dir on Linux

[dimitri-b]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

To reproduce, on Linux OS:

• build a config manager that subclasses BaseSettings
• add secrets_dir config pointing to dir with text file(s), as per docs
• add class attributes to use the files in secrets_dir, as per docs
• run the code and inspect/print the attributes
• observe that vars coming from .env file work fine, but those from secrets_dir are None, or error if not Optional, and there is no user warning for the secrets_dir itself

Repeat the same on MacOS - it should work OK, the content is read correctly.

I have added a repo with Dockerfile replicating the setup: https://github.com/dimitri-b/pydantic-secrets-dir-issue

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.8.2
            pydantic compiled: True
                 install path: /usr/local/lib/python3.8/site-packages/pydantic
               python version: 3.8.12 (default, Sep  3 2021, 02:35:42)  [GCC 8.3.0]
                     platform: Linux-5.10.47-linuxkit-x86_64-with-glibc2.2.5
     optional deps. installed: ['dotenv', 'typing-extensions']

import pydantic

class SettingsLocal(pydantic.BaseSettings):
    NORMAL_VAR: Optional[str]
    SECRET_VAR: Optional[str]

    class Config:
        env_file = "./.env"
        secrets_dir = "./secrets-in-project"
...

[grelinfo]

I've got the same bug bug solved with config case_sensitive = True