Audit Self-Test Aborts on Windows at the Invalid-Byte Filename Probe #3338

Defect

python3 spec/audit.py --selftest aborts on Windows with CalledProcessError from git add -A (exit 128) in the hub_tracked invalid-byte filename probe in _selftest_cases, because the probe's non-UTF-8 name is created but git cannot add it there. The Windows unit test job surfaced it when a new test ran the self-test as a subprocess (found on the pull request for the git location helper). The probe catches OSError on creating the file but not a failing git add.

Expected

The probe skips on a host where git cannot add the name, as it already does where the file cannot be created.