tests: add guard check for suid support This adds a check for setuid and setgid support and guards a part of a test requiring this particular filesystem feature. Such feature is notably missing in the Nix/NixOS build sandbox and was causing the whole test to fail for the mercurial package. Differential Revision: https://phab.mercurial-scm.org/D11739

[build-system]
requires = ["setuptools", "wheel"]

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