i18n: fix coding tag unsupported by xgettext Running `make update-pot` currently fails with the following error: xgettext: mercurial/metadata.py:1: Unknown encoding "utf8". Proceeding with ASCII instead. xgettext: Non-ASCII string at mercurial/metadata.py:311. Please specify the source encoding through --from-code or through a comment as specified in http://www.python.org/peps/pep-0263.html. Differential Revision: https://phab.mercurial-scm.org/D9260

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