Add CI job for pytest development version

[evjames4]

Closes #1132

This adds a separate CI job to test pytest-asyncio against the development version of pytest while keeping the existing stable test matrix unchanged.

Summary:

• adds a new GitHub Actions job for pytest dev testing
• uses a reduced Ubuntu/Python 3.13 setup
• runs tests via tox to match existing workflow
• includes coverage artifact handling
• updates the check job dependencies accordingly

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.53%. Comparing base (b6f574c) to head (ba4e4c5).
⚠️ Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1429      +/-   ##
==========================================
- Coverage   95.13%   94.53%   -0.61%     
==========================================
  Files           2        2              
  Lines         473      512      +39     
  Branches       57       61       +4     
==========================================
+ Hits          450      484      +34     
- Misses         17       22       +5     
  Partials        6        6              

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[seifertm]

Thanks for the contribution @evjames4 !

It's desirable to have parity between the CI/CD workflow and the local development environment. That means, it should be possible to run the tests against pytest dev in the local development environment.

There was another Pull Request which seems like it had this figured out. Can you take a look and extend the local development environment so that there's a tox environment that runs all tests against the development version of pytest?

[seifertm]

I don't think we want to make this a mandatory CI job. It's completely fine to merge code, even though test-pytest-dev does not run successfully.

We want to have the CI job to make incompatibilities visible only, not to block on them.

Suggested change

	needs: [build, lint, test, test-pytest-dev]
	needs: [build, lint, test]

[seifertm]

Let's just use the PYTHON_LATEST, in order to keep Python updates in the workflow simple.

Suggested change

	python-version: '3.13'
	python-version: ${{ env.PYTHON_LATEST }}

[seifertm]

Suggested change

	name: ubuntu - Python 3.13 - pytest dev
	name: ubuntu - Python ${{ env.PYTHON_LATEST }} - pytest dev