Fix type hint in setuptools/unicode_utils.py

Author: abravalheri

setuptools/unicode_utils.py

@@ -66,7 +66,7 @@ def _read_utf8_with_fallback(file: str, fallback_encoding=py39.LOCALE_ENCODING)
 
 def _cfg_read_utf8_with_fallback(
     cfg: ConfigParser, file: str, fallback_encoding=py39.LOCALE_ENCODING
-) -> str:
+) -> None:
     """Same idea as :func:`_read_utf8_with_fallback`, but for the
     :meth:`ConfigParser.read` method.