test_summary: count pytest xfailed/xpassed so expected-fail runs are observed - #41

Pytest summary lines can name expected failures and unexpected passes:

2 xfailed in 0.12s
1 passed, 2 xfailed, 1 xpassed in 0.40s

parse_pytest_summary_line only counted passed / failed / error(s) / skipped. An xfailed/xpassed token was ignored, so a run whose only outcomes were expected failures returned None — and ObservationBuilder then recorded no test_results for that worker output. The factory looked like the worker never ran tests.

A mixed line undercounted too: 1 passed, 2 xfailed became passed=1, total=1 instead of three known outcomes.

Change: treat xfailed and xpassed like skipped (known non-failing outcomes on the summary line). Warnings and deselected counts stay ignored. Docstring updated.

Tests: two cases in test_parse_pytest_summary_line_exact_outcomes. Both fail on main and pass with this change.

python -m pytest -q tests/test_test_summary.py   # 36 passed
python -m ruff check src/foreman/test_summary.py tests/test_test_summary.py