Rich renders the banner panel with box-drawing characters (╭, ╮, │, etc.)
that cp1252 cannot decode. On Windows, subprocess.run(..., text=True) uses
cp1252 by default, so decoding the child stdout raises UnicodeDecodeError
and subprocess sets result.stdout to None — breaking the assertion with a
misleading "argument of type 'NoneType' is not iterable".
Pass encoding="utf-8" explicitly so the test passes on every platform.
