run-tests: use byte strings for inserted output
We were inserting str on Python 3 which resulted in mixed
str/bytes types on the list. This would later blow up when
trying to write str to the .err file opened in bytes mode.
Differential Revision: https://phab.mercurial-scm.org/D7222
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
| contrib/python-zstandard/
'''
skip-string-normalization = true
quiet = true