use UTF-8 encoding in unit test test_output_to_file

[oxygen dioxide (oxygen-dioxide)]

On my Chinese windows, this test fails with the following error:

        with open(output_file, "r") as f:
>           output_data = f.read()
                          ^^^^^^^^
E           UnicodeDecodeError: 'gbk' codec can't decode byte 0xaa in position 61: illegal multibyte sequence

tests\test_cli_vectors.py:87: UnicodeDecodeError

because Markitdown writes to file in UTF-8, but the test tries to read it in local encoding

[Adam Fourney (afourney)]

Thanks for identifying the locale-dependent decoding failure in test_output_to_file. #2351 incorporated the same correction: the test now reads the generated output with an explicit UTF-8 encoding.

The change is on main, so I'm closing this PR as already addressed. Thank you for contributing the fix.