Add test for non-ASCII characters in pyproject.toml

[cjolowicz]

poetry.Config incorrectly used Path.read_text without specifying UTF-8 as the
encoding. On systems with a non-UTF-8 locale, this can lead to decoding errors
because the preferred encoding on the system would be used to decode the
contents of pyproject.toml. This can result in garbled configuration values or
a UnicodeDecodeError exception. For example, the character Á will fail to
decode on Windows systems with CP-1252 as the preferred locale encoding.

See #233

[cjolowicz]

For the record, here's the output of the failing test on the Windows runner, before this PR was rebased on the merged fix:

================================== FAILURES ===================================
____________________________ test_config_non_ascii ____________________________

tmp_path = WindowsPath('C:/Users/runneradmin/AppData/Local/Temp/pytest-of-runneradmin/pytest-0/test_config_non_ascii0')

    def test_config_non_ascii(tmp_path: Path) -> None:
        """It decodes non-ASCII characters in pyproject.toml."""
        text = """\
    [tool.poetry]
    name = "�frica"
    """
    
        path = tmp_path / "pyproject.toml"
        path.write_text(text, encoding="utf-8")
    
>       config = poetry.Config(path.parent)

tests\unit\test_poetry.py:17: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
.nox\tests-3-9\lib\site-packages\nox_poetry\poetry.py:24: in __init__
    text = path.read_text()
c:\hostedtoolcache\windows\python\3.9.1\x64\lib\pathlib.py:1256: in read_text
    return f.read()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <encodings.cp1252.IncrementalDecoder object at 0x00000210B56FBBE0>
input = b'[tool.poetry]\r\nname = "\xc3\x81frica"\r\n', final = True

    def decode(self, input, final=False):
>       return codecs.charmap_decode(input,self.errors,decoding_table)[0]
E       UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 24: character maps to <undefined>

c:\hostedtoolcache\windows\python\3.9.1\x64\lib\encodings\cp1252.py:23: UnicodeDecodeError
=========================== short test summary info ===========================
FAILED tests/unit/test_poetry.py::test_config_non_ascii - UnicodeDecodeError:...
================== 1 failed, 29 passed in 102.56s (0:01:42) ===================

[staticdev]

@cjolowicz thanks a lot for the release and also for making the proper tests. My bad I didn't have time to make a better job.

I really appreciate your open-source work. Great engineer you are =)

[cjolowicz]

Thank you 😊