Pendulum reports FileNotFound error when local timezone set with env var on Ubuntu

[egbutter]

• I am on the latest Pendulum version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• Ubuntu 19.10 (eoan)

• Pendulum 2.1.0

• Timezone set via environment variable, TZ=UTC

Issue

• Ran a test that relies on pendulum
• Test calls pendulum.now().timestamp()
• Expected: current seconds since epoch for local computer timezone
• Actual: traceback below - suggests that pendulum is trying to open a file with the name "UTC" instead of using the environment variable value "UTC" to set the timezone in pendulum

Traceback (most recent call last):
  File "/home/egbutter/.pyenv/versions/xxx/bin/pytest", line 10, in <module>
    sys.exit(main())
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/_pytest/config/__init__.py", line 125, in main
    config=config
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/manager.py", line 87, in <lambda>
    firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/callers.py", line 208, in _multicall
    return outcome.get_result()
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/_pytest/main.py", line 240, in pytest_cmdline_main
    return wrap_session(config, _main)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/_pytest/main.py", line 213, in wrap_session
    config.notify_exception(excinfo, config.option)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/_pytest/config/__init__.py", line 864, in notify_exception
    funcargs=True, showlocals=getattr(option, "showlocals", False), style=style
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/_pytest/_code/code.py", line 619, in getrepr
    self.type, self.value, self.traceback[0]._rawentry
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/traceback.py", line 121, in format_exception
    type(value), value, tb, limit=limit).format(chain=chain))
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/traceback.py", line 508, in __init__
    capture_locals=capture_locals)
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/traceback.py", line 363, in extract
    f.line
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/traceback.py", line 285, in line
    self._line = linecache.getline(self.filename, self.lineno).strip()
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/linecache.py", line 16, in getline
    lines = getlines(filename, module_globals)
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/linecache.py", line 47, in getlines
    return updatecache(filename, module_globals)
  File "/home/egbutter/.pyenv/versions/3.7.5/lib/python3.7/linecache.py", line 142, in updatecache
    size, mtime = stat.st_size, stat.st_mtime
  File "/home/egbutter/sandbox/modern/yyy/tests/pdf_scraper_test.py", line 13, in st_mtime
    return pendulum.now().timestamp()
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/__init__.py", line 211, in now
    dt = _datetime.datetime.now(local_timezone())
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/__init__.py", line 60, in local_timezone
    return get_local_timezone()
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/local_timezone.py", line 35, in get_local_timezone
    tz = _get_system_timezone()
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/local_timezone.py", line 63, in _get_system_timezone
    return _get_unix_timezone()
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/local_timezone.py", line 157, in _get_unix_timezone
    return _tz_from_env(tzenv)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/local_timezone.py", line 253, in _tz_from_env
    return TimezoneFile(tzenv)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/timezone.py", line 370, in __init__
    tz = read_file(path)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/zoneinfo/__init__.py", line 16, in read_file
    return Reader(extend=extend).read(path)
  File "/home/egbutter/.pyenv/versions/3.7.5/envs/xxx/lib/python3.7/site-packages/pendulum/tz/zoneinfo/reader.py", line 65, in read
    with open(file_path, "rb") as fd:
FileNotFoundError: [Errno 2] No such file or directory: 'UTC'