[bug] Pydantic upgrade breaks timezone config

[signebedi]

I was able to verify that it is the pydantic version that breaks this test, because whereas the older version 2.7.1 had no issue with the field validator I had set up, an upgrade to the most recent version (2.9.0), did:

pip install -U pydantic
Requirement already satisfied: pydantic in ./venv/lib/python3.10/site-packages (2.7.1)
Collecting pydantic
  Downloading pydantic-2.9.0-py3-none-any.whl (434 kB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 434.3/434.3 KB 515.2 kB/s eta 0:00:00
Requirement already satisfied: tzdata in ./venv/lib/python3.10/site-packages (from pydantic) (2024.1)
Requirement already satisfied: annotated-types>=0.4.0 in ./venv/lib/python3.10/site-packages (from pydantic) (0.6.0)
Requirement already satisfied: typing-extensions>=4.6.1 in ./venv/lib/python3.10/site-packages (from pydantic) (4.11.0)
Collecting pydantic-core==2.23.2
  Downloading pydantic_core-2.23.2-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (2.1 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 2.1/2.1 MB 4.5 MB/s eta 0:00:00
Installing collected packages: pydantic-core, pydantic
  Attempting uninstall: pydantic-core
    Found existing installation: pydantic_core 2.18.2
    Uninstalling pydantic_core-2.18.2:
      Successfully uninstalled pydantic_core-2.18.2
  Attempting uninstall: pydantic
    Found existing installation: pydantic 2.7.1
    Uninstalling pydantic-2.7.1:
      Successfully uninstalled pydantic-2.7.1
Successfully installed pydantic-2.9.0 pydantic-core-2.23.2
(venv) sig@brunhilda:~/Code/libreforms-fastapi$ uvicorn libreforms_fastapi.app:app --reload
INFO:     Will watch for changes in these directories: ['/home/sig/Code/libreforms-fastapi']
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [16575] using WatchFiles
Process SpawnProcess-1:
Traceback (most recent call last):
  File "/usr/lib/python3.10/multiprocessing/process.py", line 314, in _bootstrap
    self.run()
  File "/usr/lib/python3.10/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/_subprocess.py", line 80, in subprocess_started
    target(sockets=sockets)
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/server.py", line 65, in run
    return asyncio.run(self.serve(sockets=sockets))
  File "/usr/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/server.py", line 69, in serve
    await self._serve(sockets)
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/server.py", line 76, in _serve
    config.load()
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/config.py", line 434, in load
    self.loaded_app = import_from_string(self.app)
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/uvicorn/importer.py", line 19, in import_from_string
    module = importlib.import_module(module_str)
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/sig/Code/libreforms-fastapi/libreforms_fastapi/app/__init__.py", line 335, in <module>
    with get_config_context() as config:
  File "/usr/lib/python3.10/contextlib.py", line 135, in __enter__
    return next(self.gen)
  File "/home/sig/Code/libreforms-fastapi/libreforms_fastapi/app/__init__.py", line 289, in get_config_context
    conf = get_config(_env)
  File "/home/sig/Code/libreforms-fastapi/libreforms_fastapi/utils/config.py", line 364, in get_config
    return DevelopmentConfig()
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/pydantic_settings/main.py", line 144, in __init__
    super().__init__(
  File "/home/sig/Code/libreforms-fastapi/venv/lib/python3.10/site-packages/pydantic/main.py", line 211, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
  File "/home/sig/Code/libreforms-fastapi/libreforms_fastapi/utils/config.py", line 111, in validate_timezone
    tz = ZoneInfo(v)
  File "/usr/lib/python3.10/zoneinfo/_tzpath.py", line 67, in find_tzfile
    _validate_tzfile_path(key)
  File "/usr/lib/python3.10/zoneinfo/_tzpath.py", line 80, in _validate_tzfile_path
    if os.path.isabs(path):
  File "/usr/lib/python3.10/posixpath.py", line 62, in isabs
    s = os.fspath(s)
TypeError: expected str, bytes or os.PathLike object, not ZoneInfo

Originally posted by @signebedi in #344 (comment)