tests: clarify some missing output in test-merge-subrepos
This makes the test behavior clearer, especially, why the output are
inconsistent.
Differential Revision: https://phab.mercurial-scm.org/D10136
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true