localrepo: fix conversion of exceptions to strings flagged by pytype This is the same as e571fec5b606. I assume the 3 similar uses of `bytestr` in `__getitem__()` are OK (even though pytype also flags them), because there is apparently test coverage for 2 of the 3 cases. Differential Revision: https://phab.mercurial-scm.org/D10131

[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true