Silence deprecations in Python 3.14

[seifertm]

Silences deprecations of:

• asyncio.get_event_loop_policy()
• asyncio.set_event_loop_policy()
• asyncio.set_event_loop()

Although this is not a permanent fix, it prevents people from having to deal with deprecation warnings caused by pytest-asyncio when testing against Python 3.14.

A long-term solution to the deprecations involve:

• a better configuration API for the loop policy (see event_loop_policy for single test #1101)
• deprecating the existing event_loop_policy fixture
• using asyncio.Runner to run the tests

Closes #1025

[seifertm]

The changes were successfully tested locally using Python 3.14-alpha7.
The CI run references the Python version 3.14-dev, which pulls in the latest development version (3.14-beta1).

Either we block this PR until tox-dev/tox#3523 is addressed or we pin the version of Python 3.14 to "3.14-alpha7" in the CI.

[webknjaz]

Could also mark non-final versions as allowed to fail.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.93%. Comparing base (af3b32d) to head (6f197a5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1111      +/-   ##
==========================================
+ Coverage   89.63%   89.93%   +0.30%     
==========================================
  Files           2        2              
  Lines         434      447      +13     
  Branches       53       53              
==========================================
+ Hits          389      402      +13     
  Misses         30       30              
  Partials       15       15              

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[bdarnell]

I'm not sure if this makes a difference for pytest-asyncio, but FYI set_event_loop is no longer deprecated. The warnings are gone in 3.14b1, see python/cpython#130322. (The policy functions are still deprecated).

[hugovk]

Either we block this PR until tox-dev/tox#3523 is addressed ...

This has now been fixed in tox: https://github.com/tox-dev/tox/releases/tag/4.26.0

[seifertm]

@bdarnell I wasn't aware that the deprecation of asyncio.set_event_loop was reverted. Thanks for sharing the discussion!

I don't think it's relevant for pytest-asyncio, because the current plan is to transition everything to asyncio.Runner.