upd: tests workflow

[abhijithneilabraham]

1. .github/workflows/test.yml — bumped the matrix to Python 3.11/3.12, and
   changed the install step to pip install ".[dev]" (the plain pip install . was
   also missing pytest-asyncio, which the test suite requires via asyncio_mode =
   "auto").
2. tests/test_tool_decorator.py — its _run() helper used the deprecated
   asyncio.get_event_loop(), which raises RuntimeError on Python 3.12 with no
   existing loop. Fixed to asyncio.run(coro).