Enforce UTF-8 encoding for linter subprocess on Windows

[akaihola]

On Windows, linting UTF-8 files with non-ASCII characters fails. This patch enforces UTF-8 encoding when calling linter subprocesses.

$ graylint -L pylint src
Exception on node <Call l.341 at 0x1fb7ece0610> in file 'tmp437lpsx3\baseline-revision\darkgraylib\src\darkgraylib\tests\test_git.py'
Traceback (most recent call last):
  File "pylint\utils\ast_walker.py", line 91, in walk
    callback(astroid)
  File "pylint\checkers\refactoring\refactoring_checker.py", line 1161, in visit_call
    self._check_use_dict_literal(node)
  File "pylint\checkers\refactoring\refactoring_checker.py", line 1727, in _check_use_dict_literal
    self.add_message(
  File "pylint\checkers\base_checker.py", line 153, in add_message
    self.linter.add_message(
  File "pylint\lint\pylinter.py", line 1270, in add_message
    self._add_one_message(
  File "pylint\lint\pylinter.py", line 1228, in _add_one_message
    self.reporter.handle_message(
  File "pylint\reporters\text.py", line 161, in handle_message
    self.write_message(msg)
  File "pylint\reporters\text.py", line 154, in write_message
    self.writeln(self._fixed_template.format(**self_dict))
  File "pylint\reporters\base_reporter.py", line 45, in writeln
    print(string, file=self.out)
  File "Python311\Lib\encodings\cp1252.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeEncodeError: 'charmap' codec can't encode characters in position 145-148: character maps to <undefined>
Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='cp1252'>
OSError: [Errno 22] Invalid argument
ERROR:graylint.__main__:'utf-8' codec can't decode byte 0xe9 in position 2838: invalid continuation byte (123)
Traceback (most recent call last):
  File "graylint\src\graylint\__main__.py", line 29, in main_with_error_handling
    return main(argv)
           ^^^^^^^^^^
  File "graylint\src\graylint\__main__.py", line 53, in main
    linter_failures_on_modified_lines = run_linters(
                                        ^^^^^^^^^^^^
  File "graylint\src\graylint\linting.py", line 423, in run_linters
    # 10. first do a temporary checkout at `rev1` and run linter subprocesses once for
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "graylint\src\graylint\linting.py", line 562, in _get_messages_from_linters_for_baseline
    tmp_path = Path(tmpdir) / "baseline-revision" / root.name
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "graylint\src\graylint\linting.py", line 473, in _get_messages_from_linters
    """

  File "graylint\src\graylint\linting.py", line 351, in run_linter
    #     modified or unmodified, to get current linting status in the working tree
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen codecs>", line 322, in decode
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe9 in position 2838: invalid continuation byte