config: re-calculate absolute %include path in `include` callback
This removes the last user of the `abs` argument for the `include`
callback. The next patch will remove the argument.
Differential Revision: https://phab.mercurial-scm.org/D8795
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true