Failing unit test

The test_check_modules test fails with the following stacktrace:

FAILED                           [100%]error reading C:\dev\imod-python\imod\tests/..\mf6\npf.py, with error: 'charmap' codec can't decode byte 0x9d in position 11658: character maps to <undefined>

test_code_checks.py:27 (test_check_modules)
def test_check_modules():
        test_directory = os.path.realpath(os.path.dirname(os.path.abspath(__file__)))
        paths = glob(test_directory + "/../**/*.py")
        ok = True
        for path in paths:
            if test_directory in os.path.realpath(
                path
            ):  # if it's a test we don't care. this very file contains print statements itself.
                continue
            try:
                with open(path) as f:
                    content = f.read()
                    try:
                        tree = ast.parse(content)
                        module_ok = check_ast(tree, path)
                        ok = ok and module_ok
                    except Exception as e:
                        print(f"parsing error in {path}, with error: {e}.")
                        ok = False
            except Exception as e:
                print(f"error reading {path}, with error: {e}")
                ok = False
>       assert ok
E       assert False

test_code_checks.py:50: AssertionError