avoid asyncio bug in 3.12.8

[arvidn]

Purpose:

Avoid the following asyncio bug, introduced in python 3.12.8:

.venv/lib/python3.12/site-packages/anyio/pytest_plugin.py:160: in pytest_pyfunc_call
    runner.run_test(pyfuncitem.obj, testargs)
.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py:2316: in run_test
    self._raise_async_exceptions()
.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py:2220: in _raise_async_exceptions
    raise exceptions[0]
/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/staggered.py:108: in run_one_coro
    exceptions[this_index] = e
E   NameError: cannot access free variable 'exceptions' where it is not associated with a value in enclosing scope

python/cpython#128479

Current Behavior:

New Behavior:

Testing Notes: