tests: bypass worktree guard in port check unit tests
After 745ea06 and c2610f8d added the worktree-skip branch to port_5015_free_check, test_ok_when_port_free and test_fail_on_lsof_timeout can short-circuit before reaching the lsof probe path when the suite runs from a git worktree. Patch both tests to monkey-patch import_install_guard to raise ImportError so they exercise the bare except Exception: pass fall-through they were written to cover. No production code changes.
Co-authored-by: OpenAI Codex <codex@openai.com>