Improve output with invalid asyncio_mode

[The-Compiler]

Instead of a long INTERNALERROR> stack trace, output a proper error
message:

$ pytest -o asyncio_mode=True
=================== test session starts ====================
platform linux -- Python 3.11.3, pytest-7.3.1, pluggy-1.0.0
ERROR: 'True' is not a valid asyncio_mode

See pytest-dev/pytest#11083

[The-Compiler]

The Python 3.12 failure is unrelated:

ImportError while loading conftest '/home/runner/work/pytest-asyncio/pytest-asyncio/tests/conftest.py'.
  /usr/lib/python3.12/ast.py:407: in visit
      return visitor(node)
  /usr/lib/python3.12/ast.py:407: in visit
      return visitor(node)
  /usr/lib/python3.12/ast.py:407: in visit
      return visitor(node)
  /usr/lib/python3.12/ast.py:584: in _new
      warnings._deprecated(
  /usr/lib/python3.12/warnings.py:5[29](https://github.com/pytest-dev/pytest-asyncio/actions/runs/5187238300/jobs/9349366651?pr=557#step:6:30): in _deprecated
      warn(msg, DeprecationWarning, stacklevel=3)
  E   DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead

• [Python 3.12] Assertion rewriting triggers DeprecationWarning pytest#10977

[seifertm]

Thanks for the PR! This definitely makes sense.

Could you also add an entry to docs/source/reference/changelog.rst? The new version can just be 0.22.0 (UNRELEASED)

[seifertm]

I adjusted the warnings filters so that the DeprecationWarnings on Python 3.12 are ignored. The CI should be green as soon as you rebase your branch.

[The-Compiler]

Improved and rebased!

[seifertm]

Great, thank you for the quick turnaround!