test_cli_entrypoint_end_to_end copies add_contributor.py with
read_text()/write_text() and no encoding argument, so both fall back to
the system locale. add_contributor.py contains UTF-8 multi-byte
characters (an em dash), which makes the read raise UnicodeDecodeError
on any non-UTF-8 Windows locale (observed on cp950 / Traditional
Chinese). The trailing mapping-file read gets the same treatment for
symmetry.
Same footgun class as the subprocess text=True sweep in #60741, just on
the pathlib read_text/write_text side.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
a619616736