commit: clear mergestate also with --amend (issue6304)
The `hg commit --amend` uses the in-memory code, which naturally
doesn't touch the merge state (well, it shouldn't anyway; I think I've
fixed bugs in that area recently). We therefore need to clear the
mergestate after calling `repo.commitctx()` since we expect that from
`hg commit --amend`.
Differential Revision: https://phab.mercurial-scm.org/D8932
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true